I have found the following information from various sources:
The DEC RRD50 drive is the same as a Phillips CM100.
A KRQ50 (M7552) is the controller for the RRD50 And RRD40.
A KRQ50 is LMSI. (LM == LaserMagnetics SI= ?Serial ?Interface)
From what you say, I would add:
Be sure the
RRD40 is the LMSI and not the SCSI version,
although this is the first I've heard of the two variants.
John A.