Go to
Amazon and type in ["CD-ROM To SoundBlaster Audio Cable"] into the search box, it will pull up several.
Its not that I think you can even "find" a DataVideo TBC-1000, but the "built-in" distribution amplifier which broke out the single input into four outputs, is another example of breaking out the video monitoring before the capture device. But in those days not only might you have a Video monitor, but also a Vectorscope, Waveform Monitor and capture device. Each had its purpose in adjusting the input signal without "loading" or disturbing the signal fed into the capture chain.
You might also decide to share the single signal source with multiple work flow chains, i.e. one VCR to feed more than one chain ect..
These days those "breakout" distribution amplifiers with their capacitors to manage the unbalanced signal inputs, are degraded and don't do their job properly, adding noise or softening the image. Like most things from back then, they need servicing after all these years. Simpler for the most part to just by pass the video amp and use it as one device with one input and one output to get the cleanest signal.
In the end though, its more likely a consumer level capture "artists" would be most concerned about the sound "design" and have their own component stereo setup with amps and mixers which they "might" want to feed into from the video capture card, and then route the result back into the sound card on the same system.
VirtualDub has a "timing diagram" strip that can be turned on under the Capture menu while in Capture mode, its only active while its actually capturing or 'test' capturing. You can watch that while not-playback listening and while playback-listening and (see) the effects of clogging the pipeline. Its rather dramatic for some cards, and not so much for others.. mostly its software and PC resource related. If the drivers are very good and the PC very fast, it won't jump around a lot while capturing with audio playback (on) but on "most" it will gyrate tremendously.
In general $1000 cards of good repute will "barely" gyrate.. trying to optimize the resource usage while struggling to keep sync and not drop frames. But less expensive cards from the day will just.. oh "forget it" they will look like ( a dance off ) with sparkling disco balls.. and lip sync will be worse than a spaghetti western.
.. if your curious.. its because a sound card is fairly "heavy duty" at resource usage, in general the less expensive the more it has to interrupt the CPU to run code to generate or capture sound. More expensive cards may offload tasks to an onboard sound card CPU, but eventually they have to use the shared resources like the hard drive and it catches up. And good vs bad drivers also factor in.. it doesn't matter if its a good card, if it doesn't actually "try" to minimize resource usage, or mishandles it badly. It can be a "middling" card and still have cheap drivers and be awful.. but that's what review sites are for.. its too bad rotten tomatoes doesn't cover sound cards.
.. video capture cards tend to have a little bit of onboard memory and a CPU/microcontroller so they can sort of work "offline" for a while.. but eventually have to use the computer bus to send or receive disk i/o and that's when it can run into a traffic jam with stuff the sound card is churning up. So.. best all around.. bang for the buck.. is to "not use audio playback" while capturing video.