"We threw the Xonar D2X (
read: gently inserted – Ed) into a variety of PCI-Express slots – it doesn’t matter what length slot you use, be it x1 or x16, the interface will automatically adapt itself to work with it. We tried the card in several systems using x1, x4, x8 and x16 slots, both PCI-Express 1.1 and 2.0, and it worked flawlessly in all of them. The bigger problem though was finding a power supply with a spare floppy connector."
http://www.bit-tech.net/hardware/2008/01/13/asus_xonar_d2x_pci-express_soundcard/2
Is this information any use to you Alf ??