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A second, related question that also concerns my four channel surround recordings-

I have a few of my 4 channel recordings where the recorded center and back stereo signal is fine, but the primary left-right pair, typically usable alone as a standard stereo recording, is not.  So I'm left with center/back only stereo recordings that I'd like to wrangle into a more listenable type of stereo.  I've considered doing a 90 degree phase shift on the back channel and then feeding the center/phase-shifted-back file into a M/S decoder such as the MSED.  Subjectively, the back channel sounds a lot like a 'side' signal with alot of indirect depth ambience.  Of course I would not expect traditional stereo with left-right imaging, but perhaps a type of stereo conveying depth and space at the outer edges around a strong center.  That would make for a more listenable recording than reproducing all the center center information from the left speaker and room ambience from the right.  I'd love to rescue these orphaned recordings.  Thoughts?

It's hard to tell.  Phase shifts which PHA-979 implements are exactly what is used when doing surround-channel into stereo conversions, but you may need to do fine-tuning - both loudness and shift degree must be fine-tuned for best results when blending surround channels into front channels.  There are formulas exists to my knowledge (do a websearch on B-format to stereo conversion), but in your case I think doing it by ear is a better approach.

Certainly by ear, I assume that may be especiakky true since these were mic'd with spaced pairs and not a coincident mic setup which I'd guess would fit more straighforwardly into ambisonic type techiques.  I'll try it.