tbh USB is probably good enough for sound cards.
If you already have a USB controller, sure. Not so much if you'd rather not spring for one just so you can use a USB sound card for which you paid still more money. I'd be surprised if there weren't 16-bit PCMCIA sound cards out there, considering how many of the things there were back in the days of 486 and early Pentium laptops. Probably just a driver issue.
(But then, I'm the kind of person who thinks putting a sound card in an Amiga is pretty silly to begin with...)
