so, have you done the ls7 swap? pics?
there really is no single card i would say is hands down 'The Best'. each card has different features and hookup options-- if at all possible, if you have the space, i would recomend a internal card(pci/pci-e, etc..) over a usb/firewire solution, and would recommend a ht omega or Maudio card (i use a esi usb card, so take it w/ a grain of salt...) over any creative solution-- creative cards seem to have driver issues that take forever to get resolved.
usb/firewire list of available cards(all of the manufacturers listed here also make internal sound cards, so you could use this list for that):
Ultimate USB, Firewire, External Soundcard List
also, are you planning on running full active through the computer, or will you be using the crossovers on the amps? if you are interested in running a active setup through the computer, look into either 'Console' or 'AudioMulch'. Both are programs that would allow you to modifiy the audio before it ever leaves the computer using vst plugins.
as far as i can tell, the programs are very similar, though, these programs are like comparing a honda civic and a toyota corrolla, or the mac/pc debate-- both do the same thing, and both have the power to do it, but have slight variations that might sway you either way. i am using console, so i feel that is the better option, but there are plenty of users here that use audio mulch, so it apparently is not a horrible program .