Your responses prompted an investigation. The short answer is that the gain on the sub was too high. The cleaner power and better cabling greatly improved my system’s resolution, top-to-bottom. What I didn’t anticipate, was how articulate below 30Hz would become – and the sub’s ability to deftly deliver it. Also, I was listening at a louder volume since the music sounded so good. Upon subscribing to Tidal, I started listening to a far wider variety of offerings – some of which went much lower than a typical double bass or electric bass guitar. This is when distortion was revealed. It seems that what was working before, didn’t any longer with the improvements.
The solution. Re-positioning the sub. A friend came over last night to help move this 125lb beast. We moved it about 4ft from its previous position. Then spent considerable time dialing in the cross-over and volume. All is good again. Sounds really nice. Also, I read an old review where the manufacturer recommended a certain interconnect specifically designed for subs – an Analysis Plus Sub Oval. Even though the distortion is gone, I ordered the IC. Will report back. Thx for the help!