What kind of Sb is it? I have a handful of Sb's around some in an old puter that I use just as a sampler, SBawe32 and 64, PCI16 and PCI512 and this AudigyI that are full duplex and work fine as such except the Awe 32 which is suppose to be full duplex but I could never get it to work as such successfully. There were versions of the SB16 in that time/era that were supposed to be full duplex yet I never had success with them acting as full duplex. Of course these cards we're released in the days of WIN3.1 and early WIN95. Still the AWE32 won't perform successfully even with the newer improved WIN versions.
Oddly, I find the PCI512 the stabilest, best sounding with the best performing AD/DA converters but creative no longer supports it in anyway, shape or form. It also has a bit weaker output than the standard SB card.
Though orginally some what misrepresented with its 24bit 96KH sampling rate advertising, the AudigyI is a fine sounding card for a budget. but stability is a joke. Installing anything audio related can thow it into chaos and send me back to the reinstalling drivers and a tweaking frenzy. From what I'm reading on the SB newsgroups the AudigyII isn't any better. I'm slowly investigating my next sound card/interface move (really wanting to do the TASCAM 488 thing) and then my buyer relationship with Creative will forever end. Their interaction with long term customers concerning this Audigy fiasco has been disgraceful by my terms.
Didn't mean to turn this so far in a different direction. SHort point was if the SB is old enough, even though it's supposed to be full duplex, it might not be performing as such.... based on my experience and thus MHO.