Last measurements look reasonable, maybe THe1 is a little high but need to check datasheets, would no explain symptoms. With parts replaced etc... I thinking that this might be a protection issue, it does match the symptoms of distorttion when volume increases past xx. Qe9,11,13,14 form an over current protection circuit driven by Re45,47. These are the "bias" emitter resistors. Could you measure the voltage drop across each resistor/one probe on each side. Anything above 500mV would be a concern. Maybe then increase the volume to distortion and redo measurement. When you try to adjust the bias, is the volume at minimum? The protection circuit should be off.