I think it also has to be mentioned that sonically, the 5.1 mix is a colossal upgrade on the stereo mix, and worth buying for that reason alone if you like the music at all. In my (humble) opinion, pretty much every BOC stereo mix sounds like hot garbage from a frequency response and dynamics perspective. It's weird, the engineering during recording is obviously good (as evidenced by how this 5.1 mix scrubbed up) but they all sound like they took a really well recorded rock album, played it through an AM radio, and recorded the output on to the master tape - no bass, no treble, all midrange and flat as a pancake dynamically. I guess it must be something to do with some of the gear that those studios were using in the mid-'70s, because the Aerosmith albums from the same period, and Rick Derringer's Spring Fever have that same kind of sound. I was going to suggest the poor sound quality of their albums being one of the reasons they never attained superstar status (I know it's certainly put me off devoting more time to their back catalog) but Aerosmith obviously did fine in spite of a similar sound, so I dunno!
