Hafler, Carver, polk and most professional mastering has a technique that actually came from MS recording techniques. A MS microphone array has a "mono" microphone and a figure 8 bipole microphone above it. The stereo spread is controlled by altering the balance of the "l+r" uniphase channel with the bipolar l-r signal. Changing the proportions in an acoustically well made recording does not "screw things up". It simply changes the balance of l+r to l-r and widens or narrows the soundstage accordingly. In many playbacks, this extends the image far to the left and right of the speakers - without losing the center image or losing bass response. As the hall ambience is random phase, it of course gets the "most" effect.
I Think that the original specification for the Hafler circuit used by Dynaco called for a 7dB lower lever for the l-r/r-l speakers. Dynacos idea of putting the "phasey" speakers behind the listener is pretty smart (if time alignment is adhered to).
Whenever I feel blue, I start breathing again.