Pre Amp break-in balance issue

I am assuming that with your previous preamp the balance was good?

I am not familiar with that preamp, but I take it that it is SS and NOT tube?  Because a weak tube in a certain socket could cause that..  What I do to verify that the signal is the same at both speakers is I put in a Cd with a test tone designed for that and then I set my multimeter to AC volts and probe + and - on one speaker and then do the same on the other and compare readings.  If I've got a real well matched pair of tubes in the balanced input sockets of my preamp, the readings are almost identical to each other. 

 but I'm learning in my old age that I don't have to have all the answers

I hear you.  I can just accept good news (in my old age) instead of questioning it.  Mostly, anyway.  Good to read that it worked out for you!