If you are talking about dual amp setups, then this is possible without any special midi gear. With a limitation: as both 11Rs by default will receive the same midi pc commands, they will switch to the same preset. So you will need to store the two amp sounds that you want to combine on the same preset. E.g. if you want a mix of a Fender Twin and a JCM 800, put the Twin sound on preset A1 in the first 11R and the JCM on A1 in the second 11R.
That would be the easiest way to set it up.
If you want to call preset A1 on the first and a different preset (e.g. A2) on the second 11R you will need a controller or a patchbay that does MIDI mapping. This is a function which creates a matrix and assigns different presets to pc commands that don't have to correspond with them. E.g. you could use MIDI pc change 001 to call preset A3 in the 11R, MIDI pc change 002 to call preset C2, MIDI pc change 003 to call preset A1 etc.
And your MIDI mapper must be capable of doing this separately for two different outputs.
I hope I was able to make clear how this should work...if not please ask again.