Join Date: Feb 2011
Location: Chandler Arizona
I will confirm that the center panel in a Model 3 is 8" wide, and the two outer panels are both 9" wide. As far as finding a replacement for the 8" panel: good luck. Not to say that they aren't available, but they are considerably more difficult to find that the 9" version.
The optimum listening position for any of the tall Acoustat models should be wherever your ears are, since they radiate equally from floor to ceiling. That is one of the beauties of that configuration. I use Spectra 4400's, and find the image and frequency response to be very stable whether I am seated or standing up. They even sound pretty good if you're laying on the floor (admittedly, not your preferred audiophile position)!
The 1+1 configuration will provide stereo imaging superior to that of any of the shorter models, but at a slight loss of efficiency and low bass response compared to the models with more panel area.
If I had to choose between a Model 3 and a Model 1+1, it would be a very easy decision for me - I would prefer the 1+1. This is an even easier decision if you already have equipment to augment the bottom end. I would recommend crossing over between 80-100 Hz, with a steep slope on the woofer system, and a first order slope (or no crossover at all!) on the ESL's.
One last thing - for the 1+1, change the low frequency transformer tap from orange (as configured for the Model 3) to the red tap, which is optimized for 2-panel systems.
Good luck...it sounds like a fun project.