As many (all?) of you know, laserdisc format allow more than a single audio track (more info could be found here: Why laserdisc soundtracks are better…)
Now, most of capture cards can grab one video source along with a stereo audio track; so, what to do with a laserdisc with more than a single stereo track?
1. capture it twice (or three times), then eventually mux the other audio track(s) to the first audio/video track
2. use more computers, each one with a capture card, to grab video along with first audio track (PC1) and video along with second audio track (PC2) – and eventually grab video along with third audio track (PC3)
3. use the capture card to grab video along with first audio track AND use further audio card(s) to capture other audio track(s)
4. use the capture card to grab video only AND an audio card with multichannel input to capture all audio tracks
Now let’s see briefly the procedures to follow to capture laserdisc with more than a single track:
-  one PC with single capture card
no single pass possible; you have to record each audio track on its own; it means that if, for example, the movie is two hours long, and it has a PCM stereo (or DTS) track, and an analog stereo track (or two mono analog tracks), it will take four hours to capture it twice; if it has an AC-3 (Dolby Digital) track, a PCM stereo track, and an analog commentary track, it will take six hours to capture it not twice, but three times!
-  more PCs each one with its own capture card
you can record first track with the first PC and its capture card, and second track with second PC and its capture card, so a two hours movie will take only two hours to be captured; still, in the case of AC-3/PCM/analog combo, you have to capture the third track in a second pass – unless one computer has two audio cards or a single multichannel cards (see next points) – OR use a third PC and its capture card.
-  one PC with two audio cards – or a capture card with its own audio capture plus a second audio card
Depending on which OS you use, it is possible to use two audio cards at the same time; on Windows (unless you use the same brand and/or model with a proper driver that allows to do that natively) you must rely on ASIO4ALL; it’s a software that let two or more audio cards work at the same time; although there could be some sync problems, many users did not report any problem at all. On MAC, you can “aggregate” two or more audio cards – do not ask me how, because I just read about it briefly and I have no idea, but I know it could be possible. On Linux, frankly I don’t know, but I guess there are not many Linux users around here with a capture card that works under this OS and with a laserdisc player…
With a laserdisc with PCM (DTS) + analog tracks, you need two stereo audio cards; with a laserdisc with AC-3 + PCM + analog track, you need three stereo audio cards, or a stereo card and an audio card with at least four channels input.
-  one PC with an audio card with multichannel input
you can capture every laserdisc ever made with this option – depending on the audio card!
With a laserdisc with PCM (DTS) + analog tracks, you need an audio card with at least four channels input; with a laserdisc with AC-3 + PCM + analog track, you need an audio card with at least six channels input.
 is the most common; many guides are written here and somewhere else; as this is the basic procedure, you HAVE to know how to do it if you want to follow another option.
 is technically relatively easy, but quite expensive; my hint is, if you already have your main PC with a capture card, just get a second very cheap used PC that will be used only for that – and eventually a third one; it’s useless to buy a brand new multicore PC with a high-end capture card and use that as second capture setup, when an hundred quid used PC could lead to the same result!
 less expensive than previous but technically a bit more difficult; the capture software could not accept more than one card at the time, so you can be forced to use two softwares (if not three) at the time, with subsequent possible problems; this last instance could occur also if you decide to use two (or three) capture cards (video+audio) instead of a single capture card (video+audio) and a second audio card; can’t know which could be less or more problematic.
 this could be the ultimate solution: a single capture card (with or without audio, it doesn’t matter) along with an audio card with multichannel input; this should avoid any problem connected with using several audio cards. But another problem is, even if multichannel audio card could be found relatively inexpensively in the used market, it’s difficult to find the right one for this procedure…
I want to go a bit deeper on  because  is not inherent to the topic grab laserdisc video and multiple audio in one pass while  is quite expensive and  could be more technically challenging.
What you can do with a  type setup?
- capture a laserdisc with two or three audio tracks in one pass, sparing:
- time – in a case of two hours movie, only two hours capture instead of four or six
- wear – mainly of laserdisc player, secondly PC/HDD etc.
- electricity – not a lot, I must admit, still some
- work – to put in sync two or three tracks
- capture a laserdisc with its own tracks AND decoded one by an external decoder
- capture two (or more) laserdiscs from two (or more) players at the same time
first two options are feasible, while last one, albeit technically possible, I’m not sure if it can work properly; leave the last aside for the moment.
So, what you need?
- a laserdisc disc with (at least) two audio tracks
- a laserdisc player with both digital and analog outputs
- optional: a laserdisc with AC-3 output AND an AC-3 demodulator, if you want to capture AC-3
- optional: an external audio decoder if you want to capture decoded audio
- analog and digital cables to connect laserdisc player to the capture card
- a computer
- a capture card (that can grab at least video)
- an audio card with multichannel input
- a capture software that can grab video AND multichannel audio
- a capture software to grab video AND another that can record multichannel audio at the same time
If you want to capture PCM and analog tracks, you need a card with AT LEAST four channels input; better if two of them are via digital input for PCM.
If you want to capture AC-3 and PCM tracks, you need a card with AT LEAST four channels input, two of them MUST be via digital input WITH bit-perfect audio for AC-3.
If you want to capture DTS and analog tracks, you need a card with AT LEAST four channels input, two of them MUST be via digital input WITH bit-perfect audio for DTS.
If you want to capture AC-3, PCM and analog tracks, you need a card with AT LEAST six channels input, two of them MUST be via digital input WITH bit-perfect audio for AC-3.
If you want to capture AC-3 and DTS tracks from a single laserdisc… well, you cant, because there are NO laserdisc with both AC-3 and DTS on the same disc!
If you want to capture PCM and analog tracks, PLUS a Dolby Pro Logic decoded track, you need a card with AT LEAST eight channels input; further two will be used for the PCM or analog tracks, and the last four ones for the L/C/R/S channels from the Dolby decoder.
If you want to capture AC-3 and PCM tracks, PLUS a Dolby Pro Logic decoded track, you need a card with AT LEAST eight channels input, two of them MUST be via digital input WITH bit-perfect audio for AC-3; further two will be used for the analog tracks, and the last four ones for the L/C/R/S channels from the Dolby decoder.
If you want to capture DTS and analog tracks, PLUS a Dolby Pro Logic decoded track, you need a card with AT LEAST eight channels input, two of them MUST be via digital input WITH bit-perfect audio for DTS; further two will be used for the analog tracks, and the last four ones for the L/C/R/S channels from the Dolby decoder.
Many multichannel cards have only one digital input, or can use it only one at the time, so in those cases you can have AC-3 and PCM but the latter will be NOT bit-perfect.
As many cards with multichannel inputs with one (or more) of them are digital (S/PDIF), are used by musicians, AFAIK their digital input *should* be bit-perfect.
- to capture AC-3 you NEED an audio card with digital input AND bit-perfect AND external AC-3 demodulator
- to capture DTS you NEED an audio card with digital input AND bit-perfect
- to capture PCM you can use an audio card (from best to worst):
- with digital input AND bit-perfect
- with digital input BUT NOT bit-perfect
- with only analog input
- to capture analog you can use any audio card
- to get DVD/BD/UHD-BD compliant audio tracks, audio cards must be at least 48kHz
Last thought: how much important is to have bit-perfect digital input for PCM track? Unless you use the result track at 44.1kHz “as is” (in which case it would be VERY important) I’m not sure how much important it will be in other cases; because if you want to mux the track to a project that will be DVD/BD/UHD-BD compliant, you are forced to convert the 44.1kHz track to 48kHz; even if this conversion has an obvious quality degradation – albeit small – could you hear the difference between a bit-perfect 44.1kHz -> converted to 48kHz and a laserdisc D/A 44kHz 16bit -> capture card A/D 48kHz 20bit (or 24 bit)? Which one will “sound better”? And we are talking about NTSC here… what’s about PAL tracks, that need also slowdown? A comparison would be very interesting!