Andrew - most McIntosh gear has a factory reset procedure. Here is the procedure for the 5300 from the manual:
————-snip————-
Reset of Microprocessors
In the unlikely event the controls of the MA5300 stop functioning, the microprocessors can be reset by performing the following:
1. Press the STANDBY/ON Push-button until the
STANDBY/ON LED Indicator switches Off.
2. Then release the STANDBY/ON Push-button and the MA5300 will switch Off.
3. When the STANDBY/ON LED is illuminated press the STANDBY/ON Push-button, the MA5300 will resume normal operation.
Note: This can be performed with the MA5300 On or in the Standby Mode.
