I have both the FM3 and the FM9, along with a FC6. And, I spend a lot of time working with both systems and thinking of their pluses and minuses, so maybe these thoughts will help.
I think it’s important to look at the use of the MC6 or the FC6 first. In the past I had the MC6, and while it’s good, it’s not as well integrated with the FM3 as is the FC6. That will probably never change; it’s not because Fractal is deliberately trying to keep that from happening, it’s just how the two different systems are built and the philosophy of how Fractal views MIDI vs. their own controllers, and it affects our view of the FM* units.
Fractal seems to view the modelers as the host, i.e., the mainframe, and the FC units as terminals; we basically type commands on the controller which tells the FM* to do something, it does it and sends a response back which updates the displays and LEDs on the controller. The MC6, being MIDI, only knows how to send commands and ask for status, it acts more like it’s always in control, and that difference affects the integration of the two systems, and it affects our view of how the systems are supposed to work together. It took me a little while to figure that difference out when I first switched to Fractal’s gear. That doesn’t mean that using MIDI is bad, it just means it’s not the native interface and will involve more work to integrate it, which Morningstar has, and will probably continue to pick up and do. But it still affects the way the two systems work.
I bought the FM3+FC6 for travel because it’s modular. I can easily use it as just the FM or add the FC for more switches and easier switching. I’m the one who worked with Studio Slips to design their FM3+FC6 bag so I can easily travel with both. The FM9 weighs the same, approximately, as the FM3+FC6, but won’t fit in as small a space. So, if you compare those two systems, the FM3+FC6 or the FM9, you have an equal number of switches plus the FM3 has more flexibility as far as form factor.
Yes, the added CPU/DSP of the FM9 is nice, but in my experience it doesn’t improve the sound quality that much, especially for live use. In the middle of a song I can’t tell that there’s improved reverb or there are two amps, because the rest of the band is filling the air with what they’re doing. The difference between economy and the highest quality reverb is really hard to hear in a band context; when recording solo guitar it’s much easier, but at that point we generally have reverb in a DAW or we can reamp and add the highest quality reverb. I keep my reverb at economy on both as a result.
I once put together a dual amp preset that sounded like something I would play with regularly, but it was so huge-sounding it would only have worked in a power-trio. The improvements to the modeling on the FM3 make it sound great in a band context so, again, dual amps don’t really improve my life.
The smaller CPU in the FM3 means I make smaller presets but I have only felt stifled once because of CPU constraint. My attitude is that it’s easy to switch presets so I can have a similar preset with the “missing” block next to the other one and in less than a second switch between them.
Well, the FM3+FC6 will beat the FM9 for inputs. I use two EV-2 or Dunlop (X) Mini, because they are small and easily packed in a bag.
In general I can do with the FM3+FC6 combination what I can with the FM9, so why do I have both? It’s the form factor on stage. My FM9 is mounted on a Temple Audio Duo 24 pedal board and is wired into their modules so the guitar and pedals connect on the right side, and the power and XLR output is on the left, and the plugs into the back of the FM9 are all low-profile to lessen the chance of damage. It’s ease of set-up and, hopefully, even more robust. Prior to getting the FM9 I had the FM3+FC6 combination mounted there but that limited the sizing flexibility.
And with the FM9 set up that way the FM3 combination is available if I want to travel light or use it on a tight stage; it’s nice to have that option.
You said you have an invitation for an FM9, but I don’t think they have any to sell right now, and they haven’t announced any improvements in availability. I suggest that you consider getting the FC6 and see how you like it. It’ll partially solve the problems you see and when they begin shipping FM9 units you can sell the FM3+FC6, or keep it and connect it to the FM9. I’ve played with that combination and it’s easy to set up a very nice layout with 15 switches.
Those are my thoughts.