I appreciate your efforts.

I've been doing a bit of reading on the potential issues that presented themselves. Well, like Alice In Wonderland, I ended up down a rabbit hole of related and unrelated things regarding recording and playback.

Back in the mid 90s, I had a Theta DAC that had a polarity switch that would allow you to reverse polarity on the fly. I tried it with several recordings and couldn't identify any changes between absolute polarity and reverse polarity. In hindsight, my system was pretty modest and my speakers were not optimally placed within my room. I've also almost always left my speaker grills in place out of caution, having kids and all, but also because I didn't notice any degradation in sound whether on or off.

This all relates to the particulars of this thread in that I've since preferred the grills off many speakers, though not all, and with the kids old enough to leave the speakers alone, I'm not worried about poking fingers and the like. Anyway, my understanding of absolute polarity being preserved in the digital domain is a crap shoot, with some claiming that a large majority of digital is intentionally polarity reversed and most digital sources are all over the map. I've also read that in the recording process, some parts of the music is recorded in reverse polarity while vocals, for example, are often times intentionally the opposite. This doesn't seem to be widely practiced with accoustic recordings as opposed to studio recordings. So, for example, the drums track could be presented in reverse polarity while the vocals preserve absolute polarity. If I'm understanding this correctly, and perhaps JA would make a few comments regarding his knowledge of recording, this would explain movement from the driver in reverse while maintaining a solid and centered vocal image. Obviously, this shouldn't be confused with your speakers being in or out of phase, which is easily apparent, but rather the presentation of the music (or at least some aspects of it) in reverse of what the microphone diaphram was doing when it was captured.

I'm still not sure whether or not I could A/B identify all tracks in absolute vs reversed polarity as I haven't made any attempts just yet. However, this would certainly explain why many songs exhibit certain desirable characteritics during playback while others seem to fall short. In particular, "Best Of" compilations are almost guaranteed to have a mix of absolute and polarity reversing songs on the disc due to their compilation nature over many studios and eras.

Fortunately, I have no bulging caps and the amp is singing beautifully. Though I didn't use a variac, I do use minimal bias when bringing an unused amp up over a few hours with 1/4 increases in bias until the final setting is reached over the last hour before putting any signals through it. More to ensure that the bias supply is stable than reforming the caps. The amps aren't that old.