You can confirm! And now it is time to turn the thanks to you!
I still a very, very light hum in a central channel (louder when my SACD player was ON, but before it had played once). I just hooked the unused channel to a dummy zone 2 cannel of my 805 and gone!
Hum... That's one for Mr. Tom!
I had actually hooked up in 6.1 before completly without hum! So it is pretty strong evidence now.
So, thanks SolidState for having done more testing (I am sort-of not confortable to play too much in the back of the A1400 as I accidentally shorted my first one moving the furniture to reach it... the spectacular firework sorts of sticks into your memory and makes you stay clear of it!
So I am very happy you did it! ).