RE: XPS 8910, sound card, installation
The only way I know of is to disable it in the Device Manager. Did you test that PCIe x1 sound card in both of the #14 PCIe x1 slots?
These were the PCIe x1 sound cards used in the XPS desktop line =
0DR8F Sound Blaster Recon3D
F333J Sound Blaster X-Fi Titanium Fatal1ty
J75NW Sound Blaster Recon3D SB1350