Well, about this, a few things from an ancient collector....:alienrob:
First, for those who want 5.1: anything recorded in 1963-64 in London was MONO ONLY. That's it, period. And even if stereo existed for anything before AFTERMATH, it wouldn't be worth the trouble in quad, let alone 5.1. In fact, if I were to guess, TSMR might be the place to start for even considering 5.1 (maybe).
AFAIK, the Stones first recorded in 3-track stereo at Chess Studios in Chicago in 1964, which is where the 5x5 is from, along with various single and Lp tracks thereafter, until....they began recording in L.A., which is where the erratic nature of Stones stereo really begins. Virtually everything they recorded *could* have been issued in stereo at the time, but wasn't--that is, until AFTERMATH, their first true stereo album (anywhere). This is where the mono on reissues is missing, from that album (US & UK editions) through LET IT BLEED. AFT, BTB, FLOWERS, TSMR, BB and LIB all had mono editions, but BB and LIB did not in the U.S.
As to the rest of the mono: most of it has been available on CD before, but there may be exceptions like "Down the Road Apiece," which was, as I remember, taken from the Mobile Fidelity vinyl box set (which also included such previously unreleased stereo mixes as "Satisfaction" and "Get Off of My Cloud," which were issued in 1984 during the first wave of Decca UK Stones reissues, which were imported to America).
Not that it has anything to do with the thread itself, I will note that the most recent Stones vinyl reissues don't necessarily match the CD editions. For instance, the SACD/CD version of 12 x 5 has half its songs (Chicago) in stereo, the other half mono. On the vinyl, it's all mono, FWIW.
Your Beatles & Stones fan forever,
ED