This is where my setup is going the opposite direction. I am using the FM9
and the FX3 together, primarily, and the one thing the FC devices don't do very well is share control capabilities between two Fractal devices.
I ended up offloading the control pedals onto an ExpressionIO (and their own board), and splitting up the button-controlled stuff between the FM9 and the FX3/FC6. The way I have the CS MIDI set on the two devices lets me share the pool of 12 CS between the two. I have a few presets where there is crossover between them (i.e., an FM9 CS controlling something in the FX3, or vice-versa), but the line between the two units, conceptually, is a thing. FM9 does my "pedals and amps", and FX3 does my "rack FX", for the most part. I did figure a way to integrate them a little more tightly by splitting the SPDIF between input mirroring on one side and full amp/cab on the other, so the possibility of a 4-amp preset is there for the doing.
What I found is that the FC6 doesn't really add much that I can really dig into to the FC9 with my setup, since my FM9 presets are, necessarily, a bit leaner and simpler. I just got a second ExpressionIO, and have plans to use it for two sliders (my F/M compensator, and one for Wet/Dry on the delays) and four switches under the board like I did on the FC6 board. That will be plenty for the FM9, and save me taking the FC6 board when using the FM9 alone. I am sure it will present some interesting extras for the FM9/FX3 rig as well....
The newer ones are metal \m/....