Actually, even though it would work with a sound blaster 16, the fact that its using the microsoft synth means that the processor is still working overtime trying to feed the information to the non-accelerated sound card while trying to process the graphics information. Now, if you have a card like mine, that somehow hardware-accelerates the soft synth; or you have a hardware-DLS-capable sound card, then the processor can focus that much more on the graphics.
Remember, it may not seem like much, but sound can still take a huge chunk of the processor time if the playback rate is 44.1khz, at 16-bit, and you're not using card that has a hardware buffer (check the test in the DXDiag tool to find if your chipset runs on a hardware buffer. Even if it does, it'll still say its loading it from a software buffer for the lower quality tests.)
Also, try disabling the EAX option. Some chipsets do a little more geometry calcution in EAX or A3D modes than what might be necessary, causing a slight drop in framerate. Hope that helps!
[edited] 239 2001-10-23 00:57