RuneAudio on the Raspberry Pi seems to deal neatly enough with the DAC powering off when idle - When you turn the DAC back on RuneAudio finds it again automatically. Thereafter it outputs via the DAC again (until it is powered off again).
This seemed to be the most relevant place to post this as I'm running the same hardware. I was wondering if there is any way to get hardware volume control for the M8 working. I'd prefer it as I spend a lot of time outside of arms reach of the volume knob