One caution about having the EHD plugged into the receiver: the reboot will be delayed 5 to 40 minutes while the receiver accesses the drive continually when it should just reboot. What it is doing I have no idea. Thus I try to be sure the EHD is off at reboot time. I do dodge the reboot time to avoid reboots while recording because not rebooting for more than 24 hours will have access problems.
I have used 2 method for multiple drives.
(1) All EHDs plugged into two power strips to switch them off and then plugging in the right color-coded USB cable, one of 8, to one of 2 722s. It is rather like the old telephone switch board. The problem is all drives get turned on and use power.
(2) All USB cables go to an unpowered 10-way hub. Then I power up one of the EHDs--no switch, just the plug. The problem is it is not easy to work both 722s at the same time. As a compromise, 2 or 3 drives have direct access to the receivers.
Three drives are used in the stand, 1 at a time, currently they are 1, 1.5, and 2TB.
Lots of permutations.
-Ken