I'm not sure if you are referring to an original Marantz 8 or 8b, or to the reissue that was produced by VAC ca. 1996. I can't comment on the reissue, but assuming you are referring to the original, I can offer some semi-relevant experience.
During the early to mid-1990s I owned a pair of Marantz 9 monoblocks, a pair of Marantz 2 monoblocks, and a pair of McIntosh MC30 monoblocks (which, obviously, differ considerably from all of the MC275 variants). Using speakers having easy to drive tube friendly impedance characteristics, the sonics of the Marantz 2's when operated in triode mode were absolutely gorgeous, and by far the best of the bunch. Using them in ultralinear mode resulted in slightly compromised sound quality in some respects, but they still sounded better than the 9's or the MC30's.
If your speakers have tube friendly impedance characteristics, and if 20 watts in triode mode or 40 watts in ultralinear mode is sufficient, and you are willing to spend what I suspect would be a bit more than twice the price of an 8B, it may very well be worth your while to wait for a nice pair of 2's to appear for sale, although that tends to be a fairly rare occurrence. If you would prefer not to wait, or if the price of a pair of 2's is prohibitive, my instinct would be to go with an 8B, if 35 to 40 watts is sufficient and if your speakers have tube friendly impedance characteristics. If you need more than 40 watts, or if your speakers have impedance characteristics that are only marginally tube friendly, go with the MC275.
Regards,
-- Al
