I've just checked the booklet, Porcy, and I'll quote what it says:
'The first three sessions in this collection were recorded in mono and in an odd kind of stereo where the rhythm section is all on one side and the entire orchestra is on the other. In addition, the enginer was getting his balance and mix for the mono master. As a result, the balance for the horns is out of whack on the 'stereo' master. Since the mono masters are beautifully mixed and sound much richer and truer to the arrangements, we have decided to use these.
The first 3 sessions (a) through (c ) cover the 'Atomic' material through to 'Splanky', 'Fan Tail' and 'After Supper'. This was the October 22 1957 session. Session (d) kicks off the 'Chairman' sessions with 'Blues in Hoss' Flat' (recorded March 4 1958).
Doesn't mention whether or not the mastering is analogue or digital but I would assume analogue. Malcolm Addey did the remastering ( ) on this in 1993 and the LPs are Q-LPs.
I can vouch that the LPs on this set sound spectacular.
I see that there's a copy of this set in the 'Motherlode' selection...