[Scott Dorsey]

hank alrich wrote:
But some of these measurements seem not always repeatable. Sometimes I
get that 12.8 V, next time I get 10 V, then 12.8 again, and so forth,
and that seems to apply to all I read at the Onkyo and Sony, but not for
the measurements made at the quadbox or power strips, which remain far
more stable.

This is because there is RF trash on those grounds, not just 60 Hz stuff,
and the meter is not reading it consistently.

What do the isolated outputs of the satellite receivers sound
like by themselves (on headphones, etc.)?

They sound okay feeding phones directly.

Bingo. And the Onkyo is fine by itself too. But when you plug them in
together, you get hum.

Stick an isolation transformer between one receiver and the Onkyo.
It won't hum, I bet.

This, incidentally, is why balanced line is used in professional installs.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."