I must not have been clear about the switch in the power module. Just remove the cover. The switch is perfectly accessible without moving the unit. I took the covers off both of my chasis. My units sit on HRS shelves with low overhead clearance, and there are no problems. I always hit mute when I flip the switch, but you can make adjustments on a CD-to-CD basis.
If you don't try it, IMO, you are missing one of the strengths of the Rex preamp.