I see you have already made a decision but for the benefit of anyone else who would stumble upon this I will give the benefit of what took me years to find out.
There is a lot more involved in quality digital recording than just an interface,(firewire or USB)
Depending on what type of mixer or preamps you have I would suggest you look at interfaces that have built in preamps (unless of course you just happen to have a Great river, RNP, Trident, or at the least a Soundcraft or Allen and Heath mixer laying around).
Signal path is crucial, and digital is notoriously merciless/unforgiving, in other words, what you put in is what you get out, so the warmer and hotter you can get it(at the lowest noise threshold) the better the result are going to be for you mixes in the long run.
If I had 2 bones to spend (which I do but use an ONYX1620 so I will just humor the thought) and I wanted to take a step up from a soundblaster card I would go with the cheapest used firewire box (like a used M-audio 410) I could get a hold of (at least 96k) that still supports and is stable with the O.S. I am using, and put the rest into a rack preamp (maybe a used ART or TNC).
OUtside of that, perhaps a MOTu MKII for now (you can usually get one for under $150 used) and invest in a quality board (if you don't already own one) or preamp later. that will get you to 8 tracks, but you will need something to drive it, some sort of preamp or mixer at the start of the signal.
keep shinin
jerm
