At the risk of sounding too "know it all," I would like to offer a comment concerning one statement. You stated that the Zen hummed because it was tube rectified. A properly designed power supply using a tube rectifier will have zero hum. Hum can also be had from other sources like heater to cathode induced hum and a poor grounding scheme. Just my 2c.

Hope you enjoy the new amp! Have fun with it!

Thermionic