Originally Posted by: knbPixels 
MultiCorder - What determines which inputs are available?
The programmers.
Originally Posted by: knbPixels 
Checking the box for "Show Unsupported Inputs" didn't add anything else to the list.
Some input types, like vMix Call (which, honestly might be the only one) are unsupported in the sense that "you can do it, but if it breaks, we warned you").
Others, like most of them, are unsupported in the sense that it flat out will not work and is not an option.
That box is for the former.
Originally Posted by: knbPixels 
Is it possible to add Zoom inputs to the MultiCorder list?
That would be the latter. In other words, no.
Originally Posted by: knbPixels 
Why is it that only SDI inputs are shown?
Supported inputs on the Multicorder are cameras and NDI.
Unsupported inputs (in the sense that you can try it and it's on you if it breaks) are, again, vMix Calls.
Unsupported inputs (in the sense that it's not even an option) are everything else.
Originally Posted by: knbPixels 
We are already using output 3 and 4 for other functionality, so only outputs 1 and 2 are available to us, giving us a max of 3 recording channels total.
Correct.
There are existing feature requests for more outputs (the option will be added when Martin, etc. feel graphics cards are stable enough to handle it) and for more input types to be available in the MultiCorder (not happening).
I'd recommend doing what I do.
4K = 4x 1080p.
3 4K recording channels will give you 12 1080p videos.
Since most cameras, and Zoom, cap out at 1080p anyway (if they even hit that), you don't lose much.
Originally Posted by: knbPixels 
If Zoom inputs were available it would be 10x more simple to select those inptus and not have to use external outputs.
It's been asked for before, and, again, the answer was "not happening". If you want to rehash it, you can, but I wouldn't get my hopes up if I were you.