I have a Sky + Box which sits on top of my Stereo Amplifier, since it has been fitted the sound from the Sky box is coming through on all the different setting ie Radio Dvd,etc..
have you got its audio outputs connected to the amp? if so, check you have not got it connected to the tape OUT socket, as this will give the symptoms you describe. try changing it to another input and see.
in any case, I would not advsie stacking anything on top of an amp. it ,must have clear ventilation as these tend to chuck out more heat than many other devices.Digiboxes also get quite hot, so i would separate them in the interests of reliability.
My Sky+ Box is connected to TV via Scart lead. When I use my Home Theatre system for playing DVD's I put Sky Box into stand-by mode.
Switch everything that is not in use into 'stand-by' or 'off' to see what difference this makes, in order to prevent cross channel induced interference.