I have been playing in rehearsal room two times with my FM9 and the FR-12, and the sound is the best sound i ever played. I play rock and hard rock. I'm using a preset with a Brit studio 20 that emulates my Marshall SV20H with a little adjustment wirth a parametric Eq that was tone matched in my computer with the real amp and using same cab.
The process is easy. Use two tracks in DAW, one for FM9 and other for real amp, then record two tracks using the same ca0b trought the FM9, conecting the amp trought input 2 to the FM9, then i use Fab filter pkugin with tone match option and it makes an EQ for match the same sound, then i use a parametric EQ with same EQ in FM9 for the emulated amp row and that's all.
I use an AB-2 switching between amp and Fm9 and the sound is 100% the same, if y close my eyes, i can't say what is the real amp or the FM9