Thanks for the input Ken!
You know, I have always stayed away from Markbass stuff for some reason or another... too popular? too ugly? or just too busy trying other gear! I have a lot of interest in the TH500, and I really like look/form of the amp. I have owned an Aggie 659/728 setup... Very well built, fantastic sounding gear no doubt.
The main reason for the interest in the LMTube for me is the 500 watt class A power section and this nice review. I really loved my Puma 500 with its Class A. Maybe I'll never notice the difference vs the TH500 class D? I dunno...
Also, someone once told me that the RS210's sound similar to the Berg HS series cabs, except for the low end compression the HS's have. If that's the case, I'm in the same camp as the OP which is something to consider I guess. I do love the sound of these RS210's... best bang for buck I have ever seen or heard!
So, now you got me thinking about the TH500 toodecisions... decisions.
Well, first, the Puma is class D (the older and new one), which is another good example of how warm and fat and organic a class D amp can sound if the designer choosed to voice it that way (and also, as an example, how the original two space class D Puma was so much more tubey, fat and organic sounding than the newer class D one space Puma, which was purposely revoiced with more mid presence and less deep bass extension... I was part of the 'field test team' on the revoicing of the newer Puma). The old Puma350 was a class A/B head, for some reason. Not sure what that one sounded like!
The LMTube is also a great sounding amp, and again (similar to the OP's impression), the 'tube' of the LMTube does very little. I would recomend the LMIII or the Big Bang as an option there, but the LMTube has a couple nice options that both those other amps don't (the additional combo jack input with volume control, and a push/pull mute).
Again, IMO, unless you are an 'all tube guy' I would be very careful in limiting options bases on solid state topology.
Finally, yes, the RS210 and the Berg HS/HD210's have a lot of similarity to me (had the RH210 and an HS210 at the same time). Nice and warm and round, and very nicely voiced for a warm sounding 'vintage meets modern' head IMO. The LMIII sounded fantastic with the RS210 to my ear. I would love to try the new Big Bang (again, very small class D, but voiced more similarly to the LMII than even the F1 was.
I can tell you right now that if I cant get the SL to brighten up and grind like the WA (which I can not)... it will never satisfy me on the gig. I afraid it's time to move on. 
