I have more experience with unplugging Quad 2905. When i moved these to my office system (which is when i bought my Soundlabs-Prostat 922), i put them on the switched power that the rest of the office was on. and it took ~30 mins for quality and volume to return to the Quads. Now i have them plugged into the UPS, so that power is never off.
The Soundlabs have only been unplugged in transporting them to my house, when i first plugged them in, no sound from one speaker and barely any volume from the other. then i paused the music and after about 20 mins i tried again and they seemed almost normal, but volume was un-even between the two speakers. later that evening i did more serious listening and the volume was fixed.