PCI-E settings and DPC latency

I wasn't sure whether to post this in video or sound cards, etc  but BIOS (and drivers) seems to be the issue so here goes:

 

 My XPS 410 worked pretty well as delivered, but since upgrading the video card (to 8800 GTS 512 (G-92) and adding 2 GB of RAM ( = 4)  and going to Vista SP1, I have terrible latency problems.

 

I generally can't move the mouse or scroll a window without making the X-FI sound crackle and sputter.  I have tried removing all usb and pci devices except keyboard and mouse, updating all drivers to latest Dell.... then latest from Creative and Nvidia, back to original Dell and now latest Dell drivers again. 

 

Based on posts in other Dell forums, I found the DPC Latency Checker and saw that even without music playing, the video demands on moving and scrolling are creating maxed latencies.

 

At the bottom of this msg I will try to post a pic of this.  Anyway,  the only config that makes the DPC probs and sound skipping go away is removing the video driver entirely and let the MS standard VGA driver load.  That seems to narrow the problem to Nvidia drivers. 

 

Creative drivers are tough to get to recognize Dell OEM X-Fi, but once they do, it seems to auto-update OK (even though the website says the auto pgm doesn't work with Vista...)  Turning on / off   EAX, SVM, XFC, bit matching,  etc  doesn't appear to have any effect on DPC. 

 

EVGA (mfr 8800GTS)  Tech Forum recommends changing m/b BIOS settings if possible to:

 

Passive Release - ENABLED

Assign IRQ to VGA - ENABLED

Delayed Transaction - ENABLED

PCI latency - 128 (or as high as possible)

 

but I don't think that works with DELL BIOS.  Only other thing I have tried is a utilty called PCI Latency Tool, but the only value that I can change is the X-FI (starts at 64, and tried 128, 256 etc).

Not sure what else there is, but if there were an onboard sound chip on the m/b, I might try pulling the X-Fi out and trying that only.  Thinking there might be some settings in Device Manager to adjust, but don't wnat to mess with that.  For now  I just turn the speakers off to avoid the sreeching.

 

Any one else having these problems or have other suggestions?  Thanks