This material appeared a while ago on the once wonderful & now defunct Xhol Desert blog; luckily, the links are still active. It was a shock to me for three reasons:
1. I never knew this session even existed, and I thought I had known everything about Faust;
2. The music, apparently improvised, has not been published anywhere else;
3. It is sooooo great! It was made circa Ravvivando, and complements the official disc perfectly.
Get this brilliant stuff in the appropriate _LAC format here (parts 1&2) and here (part 3).
Or in mp3/320 - Mediafre, 72 Mb.