Well, thanks to
@solderdude , I have a handy AB switch at my listening chair to flip phase at the preamp/amp interface.
And on most modern music it doesn't make a noticeable difference. I suspect modern recordings have many tracks in both normal and reverse phase due to many, many processing steps.
On old recordings (in my case, jazz from 1950-1960s) there is often a difference, but again not a consistent one. Vocals sound better with one phase, base sounds better with another. For music you really enjoy, listening twice is wonderful.
So a fabulous tool to have at your disposal... sometimes. It seems that in balanced equipment, where both phases are available, we should have this feature built in.
If you ask nicely and pay the modest price, he may make one for you. Nice looking, too.