I know it's less than ideal, but at least it's easy. If you plan on using the DAC, why not just use a simple 2 channel attenuator for volume on the output of the dac going into the behringer units?
Dave Navone and I think PAC makes a simple one.
David Navone N-22V
Dammit. Now I'm wanting to use the behringer units but one is affordable 2 makes it less affordable for me