Sorry for delay in responding, guys ... have been tied up with work.
Espo77 : “The question is, does the Bose have a digital coaxial input, or better yet a toslink/optical connection on both devices. The optical is pretty much a noise free connection.”
The ONLY input on my Bose SoundDock II is a 3.5mm IN socket, which I think is analogue ... so a toslink cable would presumably be no good here (I’ve just googled “toslink” and found it is for optical connections).
Espo77 : “I keep talking about controlling the two volumes on the two devices ...”
Yes, I’ve done some experimenting with that, and I can get the buzz down almost to the inaudible level – but not silent completely. I'm not sure that is the long-term solution unfortunately.
Espo77 : “... also you can come "out" of the set top box with various connections, and hook to the "in" on the Bose. This might help to trouble shoot.”
Red+white RCA jacks FROM the set top box TO the Bose (3.5mm socket) is no problem. Pure audio, no hiss/buzz/hum. It’s TV to Bose that’s the headache.
Selden Ball : “If they aren't already, plug all of your audio equipment into the same outlet (i.e. into the same power strip). Buzz/hum is usually caused by a "ground loop". This usually is caused by plugging audio equipment into two different power outlets in your home. Most homes are provided two separate power phases (of the three available) by the electric company. All audio and video equipment needs to be plugged into the same power phase.”
I’ve just checked my setup ... the Bose was in a different power socket so I collected everything (set top box, TV, and Bose) on a single power strip. I "think" there was a slight improvement but again not completely solved. There is still a fairly audible buzze from the Bose when the TV is providing the input.
Chikoo : “TV 3.5mm headphone --> Bose 3.5mm IN should work best for you.”
I’m afraid that’s one of the cables I have tried (male 3.5mm at each end) ... buzzzzz/hummmmm ...
A thought occurs to me: I bought this (Prosonic) TV in Denmark a few years ago and brought it to Scotland, where I now live ... maybe there are special electrical conditions there that differ from where I am now (although I’ve never noticed anything previously). I’ll make some inquiries on a Danish forum, see if anything turns up.