As an update. The stock ML cords have been installed on my subwoofers. So I let the system play all night on a playlist. I sat down for a bit before heading out to work. I was able to swap cables between subs and the ML. Small differences between the stock and the Pi ones. Small enough that a new sweep of the DSP program could conceivably minimize those differences even more. I will try that this evening.
But at this point it does not seem plausible that this is a good place to invest any significant money.