Frank, did you actually stack the two units and hear a hum?
Not doubting you, just willing to allow myself to start thinking about the arrival of the GSX in the current batch and want to rearrange the gear in my rack in advance. Stacking would be ergonomically ideal (and the least work!) but if current owners confirm the hum from stacking, I'll rearrange gear so they can be separated.
Approximately how long is the connector for the two components?
When I was with my Publisher comparing the Liquid Gold to the GSX he had the GSX stacked and there was an auible hum. I hear nothing that they are separated and Justin does not recommend stacking because it will hum.