Re: what sound card to buy?
I have a MOTU traveller. Really happy with it. I feel it really useful in the live sets because it has 8 analog outs and so I can have more headroom when I take sub mixes out from different analog outputs. Increases the power for sure. Also has MIDI, digital i/os, 4 mic pres etc. If it fits your budget, it's quite good. Check it out.
A smaller interface is the MOTU ultralite. I know a couple of friends who use it and are quite happy.