I’m running Yosemite 10.10.2 on a late 2013 MBP Retina. I neglected to add that the Mute checkbox was disabled when DPSReflector was the selected sound device, so I couldn’t directly unmute it. Changing the volume only changed the on-screen display and nothing else.
Interestingly, I turned DPS back on as I was writing this and volume control worked. I checked Sound preferences and noticed that Internal Speakers was still selected, so I manually switched it to DPSReflector and it’s still working (for now). I’m now curious as to A) why it’s working, B) why it’s still not selecting the DPSReflector when I turn DPS on, and C) why I can now mute & unmute the volume when DPSReflector is selected.
I did need to reboot for something last week, and I took the opportunity to reset PRAM and SMC. I’ve rebooted multiple times since this version of DPS was installed, so the fact that it’s working may have something to do with the resets.