Need to be careful, as there can be compatibility issue depending on the engine your modifying. You can wind up with the serial data corrupted and not working. This than requires a buffer, or you need to go back to the ERR RS5.0. I also have received bad Powered MB from Lionel.
The problem is the ERR products and the Powered MB isolated Serial data via opto couplers and this sometimes degrades signal. Also Jon Z did post that ERR was optimized for the ERR RS5.0. I have also done what GRJ has done, and I also have run into combinations that do not work. You can spend hours trying to resolve it.
Sometime engine works fine for a few minutes and then you loose TMCC control. So.....just be aware. G
So what your saying is sometimes the older Rs4 boards don't respond well with the newer commanders