Do you ever use the balance on your pre amp?

Yep. In the same boat as you. I don't have a symetrical set up, and I neeed either a balance control or a dual mono preamp to get the sound right. I realise it is not the purest of set ups, but it is what I need to get it right for me. I tried a dual mono preamp, but I personally just didn't like always adjusting both controls everytime I listened. With a balance control I can set it and pretty much leave it.

Ah, the tribulations of the Rich and Famous :>)
My wife and I had a standing joke about how every system we set up in our earlier years needed a twirl of the balance control to adjust for what we blamed on living at the wrong location relative to the position of the moon and planets.
Then I decided the quality control guy at each factory took his lunch break while our particular units came down the line.
You're right about a particular rightness when the listener is positioned where the recording engineer centered the image.
Next, I can predict you'll become aware of the off center (but, real) positioning of certain musicians and vocalists, who also occasionally dare to turn their heads, further complicating things.
The ultimate solution to all of this is for minimalist high end manufacturers to re-introduce the long gone balance control, this time as a remote control feature.
Meanwhile, I have pressed back into service my KLH 21 table radio whose monophonic imaging, and limited bandwidth, hide all the rough edges in any recordings.
"We don't need no stinkin' balance control."

Vote me in the Balance control camp, I have the same issue with vocals and stage right...so the slight scew is a nice option, wish I didnt need it but glad it is there.