PPI A600.2

Check the 10 ohm 2 watt resistors behind the RCAs they blow open when the amp get abused to prevent current from flowing back into the HU. I actually stock them just for this failure mode its pretty common. They may look perfectly Ok but you must ohm them out and they usually open up completely but I have seen some 1 k ohm readings before , so anything not 10 ohms replace them.
When they blow open the ground of the input is open so you can get hum and noise issues even though the amp works somewhat. Open gain pots can also cause issues similar to your description.
 
Ok must have over looked it the first time..

1 bank of the outputs get hot are the drivers on the main board or on the card?


On the 600.2 there are drivers located dead center of each bank of outputs. But what drives those are located on the SIP module. Depending on which version you have you should see plastic green and black Toshiba drivers to the outputs. They did vary by version so they might be using other devices but they will be a set of PNP and NPN drivers located dead center of the outputs...hope this helps some...
 
Ok the driver Tansistors are defective..

Dont know if theese are orginal part numbers or not they are marked

B1085A and D1562A


Is there a good replacement for the Output drivers ??


Those appear to be the original devices. I have not had to replace any in a while, and I try to stick with original parts to not introduce any abnormalities in the original design.
Perhaps Perry can suggest you a good replacement set. I would trust his judgment...