Ahah! So that’s the culprit. Yes, there’s plenty of output on the Axe III’s headphone jack. Combined with the Mo-Fi’s built-in amp, it could blow your head off.For anyone curious. Apparently the Axe-III has a different kind of output circuit, and using the built-in power amp on the Mo-Fi isn't necessary. So, mystery solved.
Thanks, Charlie w/ Fractal support!