Since psychoacoustic compression (MP3, WMA, others) relies on removing inaudible information these control signals are usually lost, unless a really low masking treshold is used. My bet would be that only a tweaked MPC --insane would retain full surround control information.
Originally posted by niktheblak Using a bit of a priori deduction, I would think that poor or too aggressive joint stereo implementations (and I don't mean just IS) especially at lower bitrates could do serious damage to a DPL sound field. Seemingly subtle stereo image distortions and quantization noise could cause pretty weird effects to the surround field. But you get what you pay for, whereas 320 kbps MP3 may indeed retain the surround field, there is no reason to expect that a 64 kbps WMA does.