So getting slightly back on the subject of ELP itself,
amazon.co.uk is now listing the mp3 versions of the expanded ELP and Tarkus reissues, so you can check out samples of what the new mixes and bonus tracks sound like. Mind you, the sound quality for these samples is TERRIBLE, so the quality is not an indication of how the final CD (and DVD) will sound, but a few notes:
1) The new stereo mix of "Knife-Edge" is about 30 sec longer than the original, so it will be cool to hear what that "extended outro" sounds like and if it will also be longer on the 5.1 mix.
2) "Promenade" is straight from ELP's Pictures set, but it's probably a studio outtake from the first album sessions.
3) "Rave-Up" sounds like a working version of what was to come on Tarkus tracks like "Mass" and "A Time and a Place". Sounds cool!
4) The Alternate versions of "Take a Pebble" and "Knife-Edge" sound like instrumental "live" tracks, while the Alternate version of "Lucky Man" does contain vocals. The "First Greg Lake Solo Version" of Lucky Man is just acoustic guitar and vocals (including harmony overdubs).
As for Tarkus:
1) The 2nd disc now contains the entire original album remixed by SW and the bonus tracks are at the end (as he himself confirmed).
2) "Oh, My Father" is a new mix. The original mix can be found on the "From the Beginning" box set.
3) "Unknown Ballad" sounds like it may be just Keith on piano AND vocals (including harmony overdubs!)
4) The Alternate Version of "Mass" sounds like an instrumental "live" track like, Pebble and Knife-Edge above.
No doubt these sound like AMAZING (and affordable) sets!