Hi Alan,
I was awaiting your response. At this point I have eliminated the tube-pre entirely and am using a single channel on my mixer and panning between the left and right channel. I have isolated the problem to be with the speakers as I've swapped the cables to and from the amp one between the other.
Furthermore, playing with the EQ on the mixer I'm 99% sure that the tweeter and mid drivers are responding identically. It is just the low frequency drivers that are contributing to this problem - although they are working.
To start with the troubleshooting, how hard would it be to swap the crossovers from one speaker to the other? Are the drivers plugged in or soldered onto the board?
