You can use a kenwood KCA-R6A remote with one of them, and disable the Kenwood remote control on the other one (option in Emplode).

However this only works in one direction. There is no built-in option to disable the Rio Remote Control.

Some creative fiddling with the Hijack IR translation features might allow you to do what you need, though. Have a mess with it at www.rtr.ca if you're up for some hacking.