Looking at the changelog of the latest firmware :

Meridian 598 Product Firmware Release 1.89.2 (2007-06-27)
New Features
None
Software Fixes - Critical - Software must be updated
None
Software Fixes - Useful - May be useful to upgrade but not essential
None
Software Fixes - Minor - Update probably not necessary
Added support for the DRL200 drive.
Fixes potential lockup due to an invalid audio mode request from a DVD.
Meridian 598 Product Firmware Release 1.89 (2005-08-09)
TBD


So, it seems like the support for DRL200 drives, was added within this firmware version.

#1 568.2mm, HD621, G91DH, 513, 511, DSP3100 , DSP33C , DSP33, 2x MJ Pro 50 MKI, M1500
#2 G68ADV, HD621, DSP3100, DSP33C, DSP33, 3x MJ Pro 50 MKII, Control 15, Vertex 2
#3 G61rsl, HD621, 596P, DSP7000, DSP5500HC, DSP33, 2x MJ Pro 50 MKII, M1500

Spare: , 2x 568.2mm, 562V.2, DSP33, Director, G55, M60.2, MS200,
Applied mods: NOS-SRx Filter by Mr. Apodizer