Well, I've noticed that splitters cut the power to both speaker sets. It works okay, though, if you don't want high volume.
My Soyo board had onboard sound, and I had both the onboard sound and an Audigy PCI card enabled. They did not conflict. I had a program for realtime voice communications that I used while online gaming. I noticed that I tended to get stuttering when I ran everything through the Audigy, so I set up the voice communications to go through the onboard sound. Then I plugged the output for the onboard sound into an old set of PC speakers I had. So, while playing a game, both sound cards worked simultaneously, but couldn't share the same output.
You might consider getting a set of USB headphones. I have a set of Plantronics sp500 with mike, and the sound is surprisingly good. It has its own digital signal processor, so it doesn't use my Audigy 2 at all. So the Audigy 2 runs my 6.1 speakers, and the Plantronics do their own thing. The headphones come with software so I can switch between the headset and the Audigy 2 in XP with a click (actually, two clicks) of the mouse button. They do not work simultaneously.
Beyond that, a good but expensive solution is the Audigy Platinum, because the front I/O drive is easier to access than the I/Os on the back...
Anyway, hope that's helps or was at least informative.
<font color=green>The Netherlands is where you go when you're too good for heaven.</font color=green> :tongue: