Stuttering and low frame rates with sound.

I have created a seperate XP (SP2) instance for my flight sim (FS9.1), and was dismayed today to discover that I had a frame rate drop with sound ("Q" in FS9) being on (12fps with it on, 22 with it off, just to give some magnitude). This became apparent when flying the DF B727, so may be dependant upon a complex aircarft (either sound or visual complexity). It is not apparent flying the default C172.My sound is a Creative Audigy 2XS. I installed the latest drivers from the Creative site, and for a bit I thought I had fixed it, so there could be a randomness related to booting here as well (I regularly boot between the older XP and this new instance, which is on D:).I've tried bring down sound acceleration,little change. IRQs are 16 for the video card and 20 for the sound card.Any ideas as to how I might proceed from here in fixing this?P4-2.661GB RAMATI 9800 Pro 128MB videoSound as stated aboveWinXP Home SP2CH yoke and rudders via USB (although PC ports are installed in the sound card).ABit BD 7 II motherbbard (home made)Thanks for any assistance,Bruce.