Yes, I actually measured the envelope expansion from DPS on a strongly compressed iMusic track, and give an example of this useful behavior (IMHO).
Regarding volume control, my observations in Audio MIDI Setup tool shows that the gains are being split between the output of DPSReflector and SoundFlower such that each gets close to the square-root of the requested gain in amplitude, or about half each in dB space. Very peculiar.
I ended up just pushing both to zero dB attenuation, and control the volume at the source, e.g., iTunes. There is some attenuation of the source arising from DPS when its processing is bypassed. I haven’t measured it precisely yet, but it seems in the neighborhood of 3-5 dB.