The FM's clean channel is a little chimier than the MK
The FM's OD channel has a little more hair than the MK.
Both are great amps! The differences are subtle
If I had to sell one of them I would keep the FM
Hope this helps

Todd

Can the MKII get close to RF tones =  IMO Yes
Is the MKII more versatile than the FM = If you consider having the HRM tonestack more versatile yes. Other than that they are not much different animals.
The Marshally description you mention I believe is for the standard HRM not the MKII. I would not consider either the FM or MK even near Marshall territory when compared to my 2550. Could probably get close with pedals though through the clean channels.

Todd

No prob

The HRM, Bluesmaster and the MKII all have the HRM tonestack which is a separate treb, mid and bass for the overdrive channel. On the original dumbles and in the C-tone versions these potentiometers are located inside the chassis so they are pretty much set it and forget it. The purpose is to be able to EQ your OD separate from your clean. This could be seen as being more versatile than the standard OTS's by some. I prefer simple and have not once thought when playing my FM ( non-HRM ) that it would be better if it had separate TMB for the OD.

The OD trim is another potentiometer that in original Dumbles was mounted internally on the pre-amp board inside the chassis and was originally set by Dumble himself when tuning the amps he built before giving them to the original buyer. Nik at one point moved the potentiometer to the back of the amp for easy access which I think is great. It is just a drive knob really but it can set the OD section anywhere from just clean boost to serious crunchy drive. I set mine somewhere in between.


Hope this helps

Todd

Hi Justie and welcome!  I have played through and have had an HRM for a couple years now.  I have run 6l6 types as well as el34 through it.  It is a wonderfully versatile stage partner, am running a c-lator with mine.  I have enjoyed being able to use the HRM trimmers, the PI trimmer, and the bias trim pot all work together to bring that amp to the kinds of tones where folks actually notice that the guitar sounds nice.  Have to say that I have adjusted the HRM trimmers only twice, am very happy now with that ability.  

Owning a D-clone is a different ride than what most folks have had, so don't be in a hurry to pick something out.  Personally, I spent quite a few hours surfing on youtube for clips, to see if I could come up with any pre purchase impressions to go with model types.  The HRM MK II came out after I had mine built, so have no experience there.  The amp taught me how to be a better guitar player, and had major influence on how I set up my other amps to play through after getting it..