Received the circuit board/controller back - amazing 8 day turnaround (even more amazing is I live in Hawaii). Excellent workmanship by Henry. Unit plays without issue...excellent sound. I highly recommend Henry for Promedia Repair.
Quick response/fix from Henry. He emailed: The problems you were hearing were from two NE5532 preamplifier integrated circuits inside the control pod, and some dirty contacts inside the volume control itself (mostly the former, though). I replaced the two ICs and was able to get a little cleaner...
I emailed Henry (htkclk@juno.com) who resides in Minn. He repairs circuit boards for the ProMedia units, including 2.1, 4.1 and 5.1. Quick reply from him with clear instructions about how to ship the board, plus exactly the type of upgrade he makes on the unit -the 4.1 system takes much less...