I’d be interested to know why a person would prefer the original RM-9 to the Mk.2 version. Dick Olsher (a favorite audio critic of mine) reviewed both, greatly preferring the Mk.2. Both reviews are available for reading in the Stereophile archives, I believe (I have a complete collection of the digest-size issues, my first subscription issue being that of Autumn 1971. It was J. Gordon Holt who changed my hi-fi life, not Harry Pearson ;-) .
In his Mk.2 versions of the RM-9, RM-10, and RM-200, Roger Modjeski successfully endeavored to lower the distortion and increase the linearity of the circuits of all three amps, resulting in improved sound quality. I know some listeners actually like the sound of high-distortion tube amps (Herb Reichert? ;-) , hence the popularity of single-ended designs in some circles.
Congratulations @dhcod! You are in a select group of lucky music lovers who have the pleasure of owning a Music Reference amplifier.