Well, I can definitely tell the difference.. especially when you have music coming out of only the back speakers, and not the front. Discrete surround sound music in particular is a pleasure of mine.. it's done two ways. The old way is to use old quad mixes and remix them to 5.1, and obviously the new way is just to issue your music natively in 5.1. The mixing itself is art in my eyes. Just the way it's all put together, the tricks and gimmicks used really amaze me... the way the surround package is produced can either enhance the music to a dimension you've never imagined before possible, or can complete destroy something that was once great.
If you guys by any chance have a surround sound system and an old PS3.. do yourself a favor and pick up the Dark Side of the Moon 30th anniversary SACD and check out the 5.1 mix.