It seems that this part of the documentary was recorded in FZ's
digital editing room, since it has some equipements for stereo
digital masters, rather than the ones for multitrack recording.
AFAIK, the combination of PCM-1630 and DMR-4000 was frequently
used in the early stage of CD mastering. Probably most of the
vast quantity of tapes shown in this footage are the "1630
digital masters", which were waiting to be edited by FZ.