How-to guide
1. Put the CXA in standby mode
2. press and hold the Speaker A/B button until the A/B lights flash alternatively and the sources A1-A4 light up.
Note: Press the Speaker A/B button once to leave the Setup menu and place the CXA back into Standby mode.
3. Make sure light A4 is on
That puts CXA in USB Audio Class 2 mode.