Firmware 18.01 introduced a new parameter in the I/O-Audio menu on the Front Panel of the Axe-Fx II. It is called the “USB Return Level” and controls the sound returning from the computer to the Axe-Fx when using the Axe-Fx as a USB Audio Interface. This sound could be iTunes, Spotify, your DAW like Cubase or Pro Tools, and even regular computer notification sounds.
If your firmware is anything before FW18.01, when you update to anything FW18.01 or higher, this new parameter will be set to a very low value of -60 dB and must be manually changed. With the -60 dB value, you will hear very little or no audio at all coming back from the computer.
Change the value to 0.00, the previous default value. If the Out Clip lights turn on while you play USB audio from the computer, turn this parameter down a bit until the clipping stops. A value of -6 or so should be sufficient.
Again, if you upgrade from FW 16 to FW 18.03, for example, you will still have to adjust this parameter since anything 18.01 or higher will introduce this issue.
However, if you’ve updated to 18.01, for example, and already set this parameter, you will not need to do it again when updating to 18.03, for example.
You can also “Reset System Settings” in the Utility menu, but this will set many other parameters to default values as well; it may be best to just change this manually.
This affects all models of the Axe-Fx II: Mark I, Mark II, XL and XL+