"I did some more troubleshooting"... Does that mean you repeated the experiment of swapping the speaker cables? And got a different result from what you reported previously? The impression I had is that swapping the speaker cable terminations AT ONE END, such that the L speaker is now driven by the R amplifier channel and upstream components, and vice-versa for the R speaker, did not move the problem from the R speaker.
But when you say you "swapped speaker cables", that could also mean that you took the R cable and used it to connect the L amplifier to the L speaker, and vice-versa. If you did that, only the speaker cables are tested. Which is correct?
But when you say you "swapped speaker cables", that could also mean that you took the R cable and used it to connect the L amplifier to the L speaker, and vice-versa. If you did that, only the speaker cables are tested. Which is correct?

