You might want to take a look at the Metric Halo LIO-8. This will take the 7.1 channel output from the Vanity93 card and will give you digital feedthrough and also perform eight channels of D/A conversions. Set the channels into a single output bus and you can control analogue output levels of all channels with the volume control. You will, however, have to use a Mac to set it up. Tonyby tcdk - Vanity93HD & Lite (discontinued)
I think that it is: FL, FR, RL, RR, .1 ,FCSBL, SBR Tonyby tcdk - Vanity93HD & Lite (discontinued)