I don't think anything is wrong with your uDAC. Typically, when I chose a digital out device (as distinguished from an analog signal out), the volume & balance control are "grayed-out." What you're describing seems normal in my experience with the sound prefs. BTW, you may also have to select the uDAC in the MIDI prefs (they're in the "utilities" folder for some reason) as well as in the sound prefs. IIRC, both need to be pointed to the device you're using to prevent unnecessary file massaging by the mac's audio. FWIW, I have seven macs in our house.
