which would be the better way of connecting a rosetta a/d to a pc?

i currently use the rosetta's S/PDIF output into the S/PDIF input of my soundcard (soundblaster platinum 5.1)

however,

I'm considering getting a firewire card for my pc, and getting the firewire expansion card for the rosetta

would the firewire connection be better than the S/PDIF connection?

i guess I'm curious if the soundcard has any effect on the S/PDIF signal?

ALSO, with the system in the question above.. I currently use ACID as a simple multi-track recorder, (no effects or editing or bouncing) and then burn the tracks as .wavs. onto CDs which then get imported into pro-tools

would using a different program like nuendo, Samplitude etc, have any sonic effect (different from acid) on the tracks themselves?