According to OMM’s Newsletter, a new Series: "from the Philip Glass Recording Archive: Theater Music Vol.I" will arrive in May. 
Included on the album is an instrumental suite from his 2003 opera, The Sound of a Voice, which I attended at its original run in Cambridge, MA.   A truly unique Glass work, it is scored for flute, pipa, violin, cello and percussion and contains some Glass compositional trademarks, but I recall part of the choice in instrumentation was interesting for the reason that none of the instruments played chords, or at least the writing for them featured Glass writing four (or five) continuous lines of music, and that, poised some challenges to the composer and the results are lovely and exciting.
The second piece on the album is Glass’ 1993 score for the play, In the Summer House.  It’s a somber lyrical score for cello and violin.  These two pieces paired together present a picture of Glass’  unknown theater pieces which I have always been curious about and have never been commerically released. Other examples in this vein have always been of remarkable quality, such as Company.

On March 30, 2007  Part 3 of OMM’s ongoing project of introducing one part per month of Philip Glass’ momunental Music in 12 Parts, in celebration of the composer”s 70th Birthday year.