Check if all components use pin 2 hot and pin 3 ground. I would suspect that one amp deviates from this configuration. Also since purchasing my VAC Renaissance preamp which is truly balanced operation, I find out that my Sony cd player and my Classe amps that utilize balanced connections are really not truly balanced as far as operation so maybe you have one component that is truly balanced with others that only have balanced connectors. The VAC has a switch which changes the grounding for the type of operation ie truly balanced or just balanced connector. If the ground switch is incorrect it can hum and or reduce output.
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