Sorry, I haven''t read this whole thread, but has the OP any idea the frequency of this 'hum'?. I know some Decware stuff can hum a little, which is no big deal normally, but I wonder if there is a room dependent frequency mode which is accentuating the in room Decware hum.
I recently moved my gear into a smaller room, and this room 'featured' a 6 db boost @ 45 Hz! I've tuned out this peak using my RME ADI-2 Dac's built in equalizer.
P.S. Decware makes some great stuff. I'm seriously considering ordering the little SE84UFO3 - despite the long wait.