Yes I too have two amps, and a giant stereo strymon laden pedalboard.
Beside not having "two amps" in the FM3 (kind of a big deal... kind of) you can still run ONE amp at your stereo split. So basically the amp inside the FM3 into all the stereo effects inside the FM3.
I can confirm the FM3 blows everything away, matches it, etc. I am not a salesman and because of personal "issues' I have not sold my giant pedalboard (thats too big a leap atm), but I can confirm the only "difference" if any is slight and really comes down to "flavour." The FM3 is definintely way better than people say, and thats saying something.
If you like "Strymon" style reverbs, btw, there are 5-6 new "cloud" verbs in the FM3.
I think youll find you can do alomost anything in the FM3, and if needing that extra "10%" them FM9.
Im on th eFM9 list and Id probably not be able to resist buying one to see what its like to even have MORE,
but ther eis a size difference... there is a physical size difference too.