It would seem to me that if you are able to mix the two together that you should not be having this problem. I would check the device manager on your computer to make sure all of the soundcard functionality is properly enabled. If you have the paperwork to the card, make sure all of the memory block locations that the soundcard could possibly use are available (always) for the sound card. Your card may also require DMA channel(s). DMA is bracketed as Hi and Low. Make sure that is configured correctly if it does require DMA. Finally, offer the soundcard its preferred IRQ exclusively which means not steered or shared at any time. I have seen some hoggish cards to require two interrupts simultaniously even. If so this is the case with yours, than so be it. If these items are not the issue, than still I would go refer back to the soundcard paperwork. If still without solution, contact the manufacturer for further support. You paid for it when you bought the hardware.
MORPH!