I believe this is Incorrect. Please reference this thread in the Fractal forum (from January 2016): http://forum.fractalaudio.com/threads/axe-fx-xl-vs-fx8-4cm.108869/...
I dont think too many have tried the 4cm with the Axe FX, from what I recall it did not work well. Sounds like you would be better off just using the Axe for amps
So the FX8 and Axe FX XL are better than the AX8 when it comes to 4CM. I tried the AX8 with 4CM and it was fine (although, that hardly counts for anything because I was using it with another modeler, not an amp). People who have use the FX8 and AX8 note that the FX8 is a bit better (slightly less noise and no coloration). Also, in comparison to the XL, the FX8 is optimized for 4CM, so it has true bypass and can do amp channel switching, which the rack units cannot.The XL+ shares the same amazing low-noise architecture of the FX-8. I regularly use my XL+ in 4CM as this is part of the modeling process. It's the quietest device I've ever tried in 4CM.
The XL units have changes that improved the noise levels in general including 4CM. Not sure, but the changes might have been introduced with the Axe FX MkII?In my 4CM experiences, with my tube amps...
Axe-Fx II MK I - noisy
FX8 - very quiet
AX8 - very quiet also. Didn't have the FX8 side by side to compare it to. But very little (if any) difference to me.