Only difference between the D2 and the D2X is one os PCI (D2), and the other is PCI-E (D2X), so you're not missing anything that way. The speaker test not working is something else. You using the latest driver
from Asus (Version: 126.96.36.1994), or the one that came on the disk with the card?
Might be worth giving this modded set a try, ASUS XONAR Unified Drivers 1.64 (post periodically updated) | brainbit
and see if that fixes it. I have a DGX and have only ever used the above since the day I got it as I had seen the reports of how flaky the driver from Asus could be.