I don't have any experience with that RF receiver, but I would assume it works fine with the XTB-IIR. The primary advantage of the XTB-IIR over the XPCR is that the former boosts the signal strength much higher than the latter. The XPCP is a coupler only and does not boost the signal strength in any way. If it works, that's good enough. The reason the XTB-IIR could potentially help is, assuming that one location had a weak signal, the repeater would amplify and repeat commands so your CM15A (or whatever you used) could see it better. I would personally eliminate all signal suckers/noise generators first since that will be more reliable. Sounds like you already did that, so it could be a signal strength issue that you simply need to fix.
Oh, there is another option if it is just the signal strength of a single module. You could get a signal booster and plug that one module into it. The boosterlinc is one option.
http://www.smarthome.com/4827/BoosterLinc-Plug-In-Signal-Booster-X10-X-10-Amplifier/p.aspxI wouldn't personally go this route since it's similar in price to an XTB-IIR and isn't as versatile. But, I'm sure there are times that this would be the best fix.