The chipset on on the card is created by C-Media. It's number is 8768. They (C-Media) compile the drivers for the hardware and the software to operate it and Diamond merely slaps their name on it.
You can either use Diamond's own drivers, included in this link: http://www.dmmdownload.com/downloads/CURRENT/SOUND/XS71series_drivers_XP_Vista_Win7.zip
Or the official C-Media drivers, included in this link: http://www.techspot.com/downloadget2.php?fid=14929_dr&f=_PCI-8738-091211-126.96.36.1990(W7-RC-01).zip
It works for both 32 and 64 bit. The software and driver are automatically installed when you double click the .exe.
Hope this helps!
P.S. I recommend the C-Media official drivers, btw.