Do you mean at the outputs of the amp/speaker connections? What value would be suitable?No, the diode is in series to each +55V and -55V of the power supplies outputs to Amplifier. The reason of adding those diode in series is to isolate both power supplies and let each power supply only charging its own capacitor.
120V/30A diode is adequate.
I should point out I'm not interested in redundant operation. I want increased power/current/va ratingSince one power supply can provide enough power, parallel two power supply will definitely increase output current capacity and also can serve the function of redundant operation.