Bob, have you ever investigated how Mid/Side stereo recordings work? Two mics are used, but not usde as a left mic and a right mic. Here's an article: http://www.uaudio.com/blog/mid-side-mic-recording/

Think of the way this amp works in reverse - playing out sound instead of recording it.

The unbaffled speaker at the bottom of the cabinet pushes sound one direction while the other side of the speaker is simultaneously 'pulling' sound. In the article above, this is like the figure 8 mic, with the out-of-phase switch enabled on the copy of that signal. With the bottom speaker, that 'phase reversal' happens naturally because the back side is exposed to the air. The speaker on the top is playing what is common to both but the back side of that speaker is enclosed in a cabinet so the 'pull' on the back side is not effectively creating sound out in the room. It's like the analog of the carioid mic that is on top. On a Mid/Side recording - you can widen and narrow the effect by the relative balance of the mid mid, versus the magnitude of the two channels of the 'Side' recording.

I've only done this a few times, when I had a Cascade FatHead ribbon mic. I tried it with acoustic guitar recordings, but found that a good-old two-mic spaced recording gave me a much easier setup (It's hard to get that M/S setup without a bunch of precise placement of mics - and both mics I tried it with had shockmounts - which makes it a little difficult to get the two capsules close - and the effect wasn't all that great on acoustic). I have since sold the Cascade - it needed a cleaner preamp than what I had available at the time.

It's not voodoo - it is a bit surprising nobody has tried this before now to be honest. It makes perfect sense as the 'playback' version of Mid-Side recording.