When I first saw this thread title, I just thought this was another baseless attempt at something that been's dead in the water for way too long, but once I realized that this petition actually has some legs to it, I gladly added my name to the list!
Obviously as already mentioned above, there could be several technical obstacles that may prove impossible to overcome, like missing multitrack tapes (and in the case of the first three records the potential for missing Quadraphonic master tapes) but even if the Quadraphonic master tapes are missing for albums 1-3, maybe they could provide us with really good transfers from released sources (like they did for the Rick Wakeman reissues).
Upmixing should only be used as a last resort (if multitrack tapes are missing for a discrete 5.1 mix and no Quadraphonic mix exists in the vaults).
One final thought would be this: besides any unreleased 5.1 mixes that are already in the vaults, would this be a project that someone like Elliot Scheiner would be involved with, and if he isn't, who would be the one to jump on board and remix any of these titles in 5.1 surround? (It probably would not be Steven Wilson...)
After this, we need inside track records to get those unreleased Elton John 5.1 mixes out in the public (and I'd love a 5.1 mix of "Who's Next" too, particularly if all tapes exist)
