Ye olde Billboard via Google Books yields another tidbit ...

Levine/CSO - Mahler #7 was RCA's first digital recording. Medinah Temple, July 1980. The Soundstream
system was used, and according to Billboard interviews with both producer Thomas Z. Shepard and
Soundstream head Thomas Stockham, it was a more elaborate setup than previous Soundstream projects.
Stockham said that his tape machine (a Honeywell instrumentation recorder) was capable of up to 8
tracks, although the typical Soundstream setup was 4 tracks and usually (in the case of Telarc at
least), it was duplicate stereo sends. For the Levine/CSO recording, Soundstream was sent 8 channels
from RCA's recording setup. So two Soundstream electronics units were sync'd together and the 8
separate digital signals were fed to the tape recorder. One can imagine how slow the editing was
with 8 tracks loaded into the DEC computer. This was all probably pushing the capabilities of the
Soundstream system. According to several different interwebs sources, the record wasn't released
until 1982. I wonder if there had to be some R&D at Soundstream to get the project edited and
mastered?

-- Tom Fine