I haven't tried using two 11R units but I have tried using one along with JamUp on an iPad. When I set up my 11R initially, I did so with the same preset types, in the same location, as my previous rig... just to make it easier to remember all my patches. I did the same thing with the iPads - so actually I can run two rigs together.
My opinion is that this works very well for the dirtier rigs... you can get a cool blending of tones and make the heavy even heavier.
Clean tones... not so much... for me, at least. For my clean sounds I try to find a tone that is particular to a type of amp, say a Fender Twin, or whatever. Blending that sound with a different clean tone seems to take away what's special about either of those clean tones. It's not that it's bad... you can certainly get away with it... but it's not special. If are going to do it, though, I would recommend putting some distance between the speakers the sounds are running through... the more stereo, the better.
That's been my experience... YMMV.