According to some postings on Headfi.org, SB Audigy 2 card resample all 44.1 kHz signal everything to 48 kHz for internal processing and then output to 44.1 kHz again. This process will introduce non-exact digital out and is quite common amoung computer sound card.
You might want to do some research on bit perfect digital output on headfi.org.
You might want to do some research on bit perfect digital output on headfi.org.