Setting the bias for the power amp section of an audio amplifier?
the power amp section is really the output stage (OPS). The input and vas stages are in the driver circuit.

the ops is quite innovative. to check bias of it, measure voltage across j/m -> should be around 4v -> 6 pn junctions.

or you can check the voltage across emitter resistors on Q16/17/19/20/22/23/25/26. they should be roughly the same.

but I doubt they are the issues. your issues sound like gain setting / protection. check r66/67/167 and c55, the input circuitry. having a signal generator + scope would be helpful.