I think part of whether someone likes the FM9 better than the Kemper is how high gain of tones you are going for. The FM9 has a lot more gain than the profiles I have for my Kemper. I don't really play super high gain tones though. Thankfully I am in a position where I can keep both of them and will. To me they are just different units that do things from different angles.
It took quite a bit of adjusting time to get the FM9 in the ballpark of the Kemper with the Dirty Shirly amp model. I have the Tone Junkie profiles of this amp and I also have a Twin Sister amp that has two of this same circuit in it. That gives me something that a lot of people don't get and that is the ability to compare the kemper and FM9 to the real amp. The Kemper is way closer to the real amp than the FM9. I have the gain down to 1.5 on the FM9 just to get in the same ballpark. The models of this amp in the FM9 have more gain than the real amp has. I bought three York Audio IR packs on black Friday. My next step will be to add a creamback IR to both units to see if that gets them closer.
What do you think about single coil cleans between the units? That's also something I care about.