VTL, ARC and the 6550C

Hello again.

I want to thank all who responded to my first post regarding VTL/Pass/Lamm. My quest for a reference system continues and I have narrowed down my choices considerably.

I will never own an ARC power amp despite my being very impressed with the VT100 going into a pair of Dynaudio speakers.

Even through the musicality was there in the VT100, ARC always sounds too cool and lean for me. They don't have the "harmonic richness" blended with detail and supurb imaging that the VTL ST150 and Marantz 8 have.

I was also surprised to learn that the 6550C tube is the same type used with both companies. Is the 6550C version of this tube better or different in sound from older variations? I have read comments about the tube being too lean which wasn't my experience at all with the VTL circuit in comparison to ARC.

The ST150 was auditioned with a CJ Premier 17LS into Thiel 2.3's which has been the best combo I have heard to date.
Seriously considering the MB 185 or MB 450 (I like triode but I prefer to have a choice so I'm bypassing the 225)

How much better are the monoblocks, discounting wattage, in terms of sound for the money when considering the law of diminishing returns? Can the MB185 also drive very current demanding larger speakers?

Thanks for reading.

D.H.