Do I have a "balance" problem?

You can also rule out your ears by simply turning around. I think it's room acoustics and speaker placement that are causing your problem. Same issue in my room, left speaker is further from the corner than the right, more rear reflection and sound is louder on that side. When I change the placement of the right speaker, the problem resolves.

I once had an amp that used a timed relay to protect the speakers from any turn on/turn off pulse. After a few years the relay's contacts degraded and affected the sound in a very similar manner. Sometimes the right channel wouldn't even play until the volume passed a threshold level, and at low volumes the left channel was always louder.

If you suspect the balance difference is your hearing. Get a good set of headphones and adjust the balance control on your preamp. If the sound is centered and the balance control is centered, the problem is in your room or speaker placement.

Speaker placement can also correct a hearing balance problem. Very small changes in speaker placement make a big audible "balance" difference in many speakers. Listen to several different recordings that have strong, left, right, and center, imaging.

I have the same problem, except my balance control has to go the 3 o'clock to lock in a center image. I had several other people listen to my system and they all preferred balance at dead center. I went to get my hearing checked hoping my right ear needed to be cleaned or something (which you should do too if you haven't already), but my ears checked out fine, which really left me scratching my head. (I also don't notice a balance problem when listening to headphones). This issue has remained through a myriad of equipment changes and in three different rooms. Pulling the right speaker forward helps somewhat, but it doesn't solve the problem and I don't like having that much of an asymmetrical speaker setup.

I noticed when I went to shows and some dealers the image was centered with the balance control set to the middle, and what I realized was that in a properly set up room the problem went away. You seem to have addressed first reflecions, but the rooms that worked for me had some sort of diffusion and/or absorption device(s) behind the system -- usually some sort of half-round tower right in the middle or something like that. I haven't tried this in my room yet but will soon. My guess is my ears are shaped slightly differently in some way, which changes their respective sensitivity to in-room reflections. If you take your hand and just change the shape of one ear slightly it's amazing how much sound changes. Anyway, that's my theory. Hope this helps and best of luck. Please let us know if you find a solution.