"I was grasping at straws to see if the system sounded better/worse with headphones; maybe more neutral by eliminating the room. A separate issue from the ringing I guess."
Its certainly worth a try just to see what happens, but not only would you be eliminating the room with headphones, but the amp, speakers, some of the cables, and possibly the preamp depending on where the headphone amp is.
Its certainly worth a try just to see what happens, but not only would you be eliminating the room with headphones, but the amp, speakers, some of the cables, and possibly the preamp depending on where the headphone amp is.