I've never run into a situation where I'd need more than one input.
If I'm doing solo stuff all I use is one input at a time.
If I record a band, I do it the same way we used to do it with our old 16 track analogue studio. Start with the drums, miked in stereo and (playing to a click so you can add midi keyboards later). Have the whole band play but only record the drums (in a drum room obviously). Then have each musician overdub his part one guy at a time.
The only disadvantage is you can't record independant rough tracks of each musician. But hopefully, before the band comes into the studio they know their material well enough that they don't need it. The tracks would be erased anyways so you just have the whole band play the tune on each run through and record one instrument at a time.
I don't think I've ever been in a studio where we didn't record each instrument separately...even going back to the real early 8 track days. We'd always spend a few hours setting up the drums and getting those down first before moving on to the other instruments.

I can see your point for multiple inputs and tracks if you're only recording live bands but most bands in the studio do it one track at a time.
And if it's absolutely necessary, just go out and get the appropriate sound cards with multiple inputs.

And what's so hard about wiring a mixer to your Mac? Take the 1/4" stereo outputs to a 1/8" plug and shove it in the input. Go to the Sound control panel and select Play Thru. You might have to do some reading up on the different ways of monitoring, but no less than you'd have to learn with a DAW.

... and I win cause I'm the bestest and smartyerist so there :cool: