MU'ing Cruise M + Cruise Commander

You have answered your own question. From what I understand both of those boards work best in the CAB1 mode. You might want to check the speed step settings on each board to make sure they are set to 32, not 100. Legacy does not like the 100 setting.

Cruise Commander can handle 4 motors so you could have tethered 2 wires to the other unit to run the motors (K-Line tether might already be there) and not have to worry about MU-ing.  Either more wires in the tether or a Mini Commander EX could handle the headlight and coupler in the other unit.

The ERR Cruise Commanders have a Nudge feature to match speeds have you tried to adjust that?

Page 6 in the ERR Cruise Commander manual explains the 'nudge' feature and how to match speeds.  I would try that first, as John suggested.  I would think that would work well, being that you have the same motor in each engine.

It worked well for me, I had a CC and a CCM equipped MTH GP-9 pair, they worked perfectly together.

Thanks, I'll try nudge and see what happens.

Part of what I seem to be experiencing is that speed step 1 is interpreted differently by the Cruise and Cruise M.  One of them starts moving but the other just revs up the RPM.  (I think;  have to go back and try it)

What is the difference between a CC & a CCM board?  I was trying to figure it out from the manuals, but to save time, can you summarize?

I'm thinking playing with the nudge feature is going to help.  It is one of the first things they mention in the manuals.

The Cruise Commander is a stand-alone product, other than the R2LC receiver board.  The Cruise Commander M is an add-on DCDR replacement for existing TMCC locomotives with modular electronics.

Got it, thanks John.  Basically for adding cruise control to a TMCC engine that was non-cruise from the factory.  Prof Chaos, make sure to report back.  Good Luck 

Yep, I've added the CCM to all my non-cruise DC motored TMCC locomotives.  Makes them behave much better.