Unsound
Funny you mentioned this back to back speaker configuration, I have often thought about this but always thought that since you were firing a driver from the rear of the speaker you would need a different type driver configuration as the sound would be traveling at twice the distance.
So funny thing I happen to have an additional pair of crossovers and upper range driver for the CS 6's, I can build a enclosure and mount the driver at the same height as the driver in the CS 6. I have a separate amp I could drive this from from the same preamp, I even has a passive preamp that I can use to adjust the volume for the experiment.
With the upcoming cooler weather I will be able to get back into my room upstairs to experiment.
I'll have to let you know how it goes.