if you want your instruments on their own channels youre going to need a lot of inputs. one solution is to buy a smaller audio interface that has optical ADAT in, and buy something like that behringer A/D converter (ada8200?) to expand your inputs. otherwise you just need a bigass audio interface.
also, using something like a mixer with multiple buses/sends can let you group several inputs together into single channels, so you wouldn't only have your stereo master outputs but actually have the mix broken into chunks you record individually