Well, I gave in and bought the SACD of the 5.1 Police greatest hits disc. Seems to be the same mix as the 5.1 - I thought what the heck, getting the hybrid disc, and it was pretty cheap.
What's a bit more odd is that I picked up Synchronicity SACD, a 2-ch, non-hybrid version. I had heard that, seeing as the CD was already really wonderful-sounding, there wasn't going to be much of a difference. I've got the Message in a Box release from a while back (a nice 4-cd set with all of their album tracks in order), and A/B'd the Synchronicity tracks with the CD release. I played through my speakers, with two pairs of studio Senheiser headphones, and, well, nuthin.
Not a damn bit of difference. I kept trying to convince myself I could hear something (I could A/B without any loss of time using a switch-box), trying double blind testing, and didn't hear a thing. There are slight differences in mastering speed, but in terms of high/low/mid-end sound, clarity, etc., etc., they sound the same.. There may be some Osciliscopic differences, but I just can not hear any difference between the SACD and the old CD release, let alone the newest remastered discs.
Wacky!