Those are nice gears. Having only heard the 600 series S2 and the CM1 S2. My impression against the S1 will be, these new versions have a smoother top end than their predecessors. I have tried the CM1 S2 w/ a variety of solid state amps(Mark Levinson, McIntosh, NAD seps from Watts Hifi), and it is not that picky unlike in the 685 S2. I'll also tell you a secret. The CM5 S1 is one of my favorte bookshelves of all time. Sound is thoroughly engaging and is flexible enough to run different types of genre with ease.
Haven't tried any CM series with tubes though, but I had extensive experience with the LM216IA having briefly owned one. It is my favorite affordable tube amp. It has that warm lush sound of tubes without giving up the dynamics we like in a solid state amp. My only gripe was the power consumption. Do you find anything wrong with your set so far?