You don't have to plug the CM15A or CM11A into the outlet on the front of the XTB-IIR.
I have my XTB-IIR near the breaker box but the controller is at the other end of the home. On one of the branch circuits.
Yes, it would work this way, too. However, if there is noise between the CM15A and the XTB-IIR, the signal might not make it far enough to get repeated properly.
I had a similar problem - CM15A needs to connect to a PC that is more than about 16 feet away (the limit of USB).
I tried a number of USB-over-CAT5 extenders, and they all had issues. They were prone to interference, which would momentarily interrupt the USB connection. Enough of these interruptions in a short amount of time would cause the CM15A to lock up in an "error" mode (as verified by my many conversations with the developers over this issue).
After consulting with Jeff Volp (the genius who created the XTB-IIR), I used an extension cord to extend the outlet on the front of the XTB-IIR, to be able to plug in the CM15A closer to the PC.
That worked, and I haven't seen any side effects (other than the orange extension cord running the length of my laundry room ceiling, marked "X10 ONLY" every few feet).
For testing, I started with a 100-foot extension cord (3-prong, the "orange" one from Home Depot). I used a 2prong-to-3prong adapter to plug it into the front outlet of the CM15A, and ran it (along the floor at first) over near the PC. I plugged the CM15A into a "standard" USB cable (I think it was about 10 feet long), and into the extension cord. I tested, and everything worked great!
Once I knew it was working, I pulled out the extension cord, and ran it across the ceiling, and down the unfinished side of the wall, to poke through into the room with the PC (I did my best to keep it neat and out of the way).
I also cut nearly all the slack off the "plug" end, and wired up a right-angle 2-prong plug. This step was also purely cosmetic. I wanted it to look more finished.
My system has been working great ever since, and I haven't had the horrible CM15A lockups I used to have.
(BTW: the outlet on the front of the XTB-IIR is two-prong, so you'd need an adapter if you want to plug the 3-prong CM11A into it. )