I have a pair of the new REF 300 MKII's. These units are FAR better than the original 300's, and in my opinion any of the 600 versions. The changes, including a change in tubes, makes this one of the best sounding tube amps out there. Haven't heard the ss AR's. AR does seem to have a propensity to frequently upgrade models, I can see how this may irritate some, but in the case of the 300MKII, what they've done is certainly an improvement.
Audio Research comparison
I'd still like to get an un-biased comparison of the old Audio Research Power Amps: VT100 MkII, VT200, REF300 and the newer solid state input versions. I have heard opinions, but they have all been self serving. So I'd like to hear from someone who has really compared the two designs. Also I'm interested in the comparison of the new pre-amp designs with the older ones LS-25 Ref2 with the MkIIs.