znalazłem coś takiego może pomoże:
"However, with the help of a friend I managed to fix this and here's how to do it. The solution lies in the Via Envy24HT chipset.
You can replace the m-audio drivers with the Envy24HT drivers (to be found here: http://www.via.com.tw/en/support/drivers.jsp).
Under Windows 7 you do the following:
open device manager
right click on M-Audio Revolution 5.1 and select "Update Driver Software..."
Select "Browse my computer for driver software"
Select "Let me pick from a list of device drivers on my computer"
Click "Have Disk..."
Browse to the correct map (in my case it was Envy24_Family_DriverV540a\VIAEnvyAud\Drivers\V64WD M). I think V64WDM stands for Vista 64bit.
Select the "Envy24 Family Audio Controller WDM" and click "Next"
This should now install the driver.
If you use SPDIF both stereo, DTS and DD should work on your pc (otherwise you cannot have stereo and DTS/DD working using the same configuration)."