USB

The Axe-Fx II's USB support is Audio Class 2.0 compliant. The USB interface supports:

1. Editing / remote control via Axe-Edit (no need for a MIDI interface)
2. Audio communication (no need for an audio interface)
3. Use as an exclusive USB-to-MIDI interface for other products (in the I/O > MIDI menu set "USB ADAPTER MODE" to ON).

Editing and recording can be done simultaneously. The Axe-Fx II cannot connect to a USB stick. Source

Drivers for Mac and PC which add support for the USB functionality are available for download here.

If you experience noise (high freq. buzzing) when using an USB connection it may be a ground loop. Cliff: "The USB spec calls for grounding the cable at both ends (mistake). This can create a ground loop. Make sure everything is plugged into the same outlet strip." Source