I don't know how large your system is or how much money you want to throw at it. As stated, I am not aware of any "ping-pong" problems with the XTB and a CM15A. I am aware of some Smarthome Boosterlinc complaints, but believe Smarthome fixed them. The Boosterlinc would bump up the CM15A output on only one phase. I would throw money at a true coupler repeater like the XTBIIR.
I have used X10 XPCR, the Leviton equivalent, ACT CR234, ACT CR230, and now the XTBIIR. The ACT units were far superior to the X10 units...but the XTBIIR trumps the ACT units with higher output.
With the XTBIIR I dumped all my filters but two. The output just blasts through most noise. I use Homeseer software with the ACT TI103 PLC interface and W800 USB for RF interface. I estimate 99.98% reliabilty
. The CM15A and AHP might be good for entry level, but just was not reliable back in 2006 and it still has miserable RF sensitivity IMHO.