Ray made four instrumental jazz albums for Atlantic:
Soul Brothers
Soul Meeting
(both with Milt Jackson)
The Great Ray Charles
The Genius After Hours
All of these are really good, although they have been on CD before, consolidated onto 3 CD's. Ray is a really fine, bluesy pianist, and these sessions feature people like Hank Crawford, David "Fathead" Newman, Kenny Burrell, etc.
The unreleased material on the box consists largely of a solo piano practice session (from 1953 I recall) that features some nice solo piano work, with Ray trying out a few things and working up a couple of tunes that he later recorded.