As has been explained by others, all E30's (or other Topping DACs) will work simultaneously with the same remote. Furthermore, if you need to control just one, then hold the remote close to that unit. From my experience, the remote doesn't have an annoyingly wide effect. We have two Vizio TV's in the basement, and either remote will control both regardless of what you do to prevent it - unplugging the power cord is the only option, which is annoying. Topping remotes are effective without being annoying.
Power the E30's using the 5v barrel adapter cord that comes with the unit. This cord is 5v barrel on one end, and male USB-A on the other end. I did not have success using the USB socket for power on the E30 - maybe it works for other folks. So use the barrel adapter cord, and plug it into any USB that provides 5v (typical USB power).
The way I'm using multiple E30's, I have theme set to -00.0 (full output), and control volume with miniDSP 4x10HD and/or NAD integrated amp/streamer.