R, on the hum problem, the first point is whether it's coming entirely from the sub or whether it's just louder from the sub because it reproduces the 60Hz hum louder than the other speakers. Set the sub(still connected and plugged in) to off and the speakers large in your 5890 to see if the hum is also in the other speakers. If it is you may have a similar ground loop problem as Jay(500)did in his thread(and apparently solved with the Parts Express isolation transformer) and should take similar steps to trace the loop. If it appears to be that only the sum hums, it isn't a ground loop an the problem is internal to the sub. If you aren't using a polarized plug(i.e. one with a bigger left prong)in a similar polarized outlet for the sub, try reversing the plug, as Alan suggested, to reverse the polarity.
