What do you mean by stability?
I do not recommend the AxeFXII as an audio interface. Not having 4 inputs via USB kills it. I use a separate interface and connect via SPDIF just like I did with the Ultra. Invest in a better card or rack unit.
This! It's reliable for a while but every so often it decides to pop and click all of my superior drummer samples when I am playing back/programing in reaper. I always just changed the sound card and then went back to to the axe and it was fine. But during a movie and game, this would be unacceptable. It'd be cool to know why this happens, if any one does know why. Be even cooler if there was something I could do to stop this from happening as it is almost guaranteed after an hour of using it.It's horrible on my systems (Macbook Pro OR Mac Pro, snow leopard - see http://forum.fractalaudio.com/axe-fx-ii-bugs/42421-mac-usb-issues.html). Least stable interface I have ever owned. Pops and clicks all over the place during any form of USB audio playback. I no longer use the axe as an interface.
:-x do u mean the inputs on the back are useless when in usb mode ?