
images via this auction
"About the Matrix 6R:
This is the rackmout version of the popular Matrix 6 keyboard synthesizer, a fundamentally superior synthesizer to both versions of the Matrix 1000:
Matrix 6 / 6R Matrix 1000
2-parts Multitimbral 1-part Monotrimbral
2 output channels 1 output channel
Edit via front panel or Sysex Cannot edit via front panel, edit only via Sysex
In addition, the Matrix 6 / 6R's oscillators produce subtle harmonic and distortion anomalies not found in the sound generated by the Matrix 1000. The Matrix 6 has a less sterile character of sound over the Matrix 1000. According to sources on the Internet, the Matrix 1000's digitally-controlled oscillators have increased tuning stability over those in the Matrix 6 / 6R, and therefore the Matrix 1000 has no Calibration feature for this reason. Around the time of the Matrix 1000's introduction, this was considered an "improvement" over the Matrix 6 design. For those of us in the 2000's hunting for more of that vintage sound, it's a bad thing! When you don't Calibrate the Matrix 6 / 6R after leaving it on for a long period of time, its overall sound contains more "chorusing" caused by ever-so-slight deviations in tuning between the oscillators and each of the 6 voices."
Hmm... This is the first I've heard of this. There have been questions regarding the M1000 vs. the Matrix-6 and 6R, but the consensus I've heard is that they are essentially the same in sound. The 6 and 6R also use DCOs. Same CEM 3396 chips.