URC training classes = you can not use the serial ports on the MRX-2 with CCP.
Literature for the MRX-2 = serial ports only work in TC and not CCP.

So I would love to know how you are able to use the serial ports on the MRX-2 under CCP. What interface are you using that allows you to do this?
Maybe there is a trick I don't know about with those? I only install basic systems for my customers with the CCP remotes.

That thread you linked to, clearly explains the difference between the jack for RS232 connections and the jack for an "IR input". They were working with a Sony TV that had both jacks on it (post #11 explained that). Most TVs do NOT have those jacks. The Samsung Frame only has an RS232 connection (no IR input jack).