I believe all music issued as stereo can be reissued as multichannel because of the original process of recording multitracks and then down mixing them into two tracks. For example, the Live at Filmore East was originally released in stereo, and with the advent of sacd and higher resolutions, the original multitrack tapes were, so to speak, taken out of the vault and re-engineered using the new formats. I believe any recordings that originated from multi tracks can be transformed as well, although, some recordings lend themselves more to the surround effect like live concerts. As to those recordings not revisited one has to use the different processes that have been included in surround sound processors such as Trifield, Dolby Prologic IIx, and Lexicon's. Although, not discrete, those processes extract enough surround sound to expand or fill in without destroying the soundstage. It's more subtle, but its analogous to listening to 256kb mp3 sound vs 364(?) mp3. A well setup multichannel system (meaning quality of the processing and matching of rear and front speakers, but not necessarily cost) is extremely important to realize the sound effect. Those who prefer 2 channel may do so because the quality of their front speakers maybe is so great as to render any rear speaker other than those of similar make unable to seemlessly integrate. For example, although price is not a primary concern, Wilson speakers or those of similar cost and unique design could be hard to match. Take a Vandersteen or Audio Physics, although well designed, is easier to integrate if not with the same make but with similar design.
