Mmm this is a bit techie/geekie but bouncing over my RSS feeds I came across a posting from NPR, that fine institution, flagged 'Attention Pink Floyd Fans'.
You can read the post as well as I can but the link off to Croz.FM had an interesting link to a download of the quadroponic mix for Dark Side of the Moon. Rather sceptically I went ahead and as Croz says the issue is not whether or not you can listen in quad (!) but the difference in the mix of the album.
I have to say that it is really noticably different (better?) - as the man says - more open, better instrument separation, effects mkore to the fore etc. BTW the site also has a great range of downloadable live shows (OK maybe not cutting edge 'now' bands but real quality)
Photo by =edmunn