While I can't speak directly to Macintosh, the technology between Mac and PC as far as audio input are more or less teh same... Software is where the big difference is...
Are you looking to record one track mixed before it hits your Mac, or individual tracks?
For pre mixed, just a stereo signal in, any USB mixer like the
Behringer XENYX Q1202USB mixer and of course yes, a headphone amp and studio headphones should do the trick. I do NOT recommend the Pyle Pro headphone amp. (Have one, it's a total warm steaming pile of....). For what it's worth, I have effectively the same mixer as that, but without the USB interface built in, and with effects added. I paid quite a bit more for my rig after the cost of the USB interface. If you want the effects on the channels, grab the
Behringer XENYX QX1202USB. $30.00 more, but if you want the effects, there they are...
For mulitrack recording, where you can do your mix down in software, I have heard the
Tascam US-16x08 is a good option, but do your homework. I have no experience with it...
IF you go with the mixer route, you have some room, although it will be crowded...
As far as cabling that might not be dead obvious, the bass amp, and guitar amp (I don't own one myself, but have had a visiting relative bring his) are connected using XLR to 1/4" TS cables. Again I do NOT recommend the Pyle-Pro headphone amp. Mine works, but it is super finicky about input. Overdrive it and everything distorts and sounds like you blew a speaker... I am seriously considering grabbing the Behringer headphone amp instead...
The UCA USB interface shown in my diagram wouldn't be in yours if you get the mixer with USB. Just use a USB A/B cable that I believe comes with the mixer.
With this particular mixer configuration, there really is no room for growth, I am more or less stuck with either daisy chaining mixers if I need inputs for mic'ed drums, OR a much larger mixer. But for my purposes into the foreseeable future, this will work fine. FWIW, mic'ed drums suck up a LOT of XLR inputs... Make the drummer buy a mixer if he wants to be mic'ed up!