Re: Fractal FX8
Reading the description, they both use the "Scenes" thing where you can change the whole layout, which I guess is the main thing that made me think of the M13. Quality and variety of effects between the two is something to consider, though, since Line6 is hung up on emulating Vintage stuff rather than producing the effect itself.
I haven't really been able to put the M13 to the test, but I believe it can do 4CM, and I know it has a EXP jack, MIDI, etc.