The RS-100 sounds rich, detailed & sweet, with plenty of control. Scot Hull (Part Time Audiophile) found the RS-100 was a good match with the Tidal Contriva Diacera SE speakers which have natural warmth, less so with the more neutral Magnepan 3.7’s. I know Joeinid on Audioshark loves the sound of his Strads with tubes (CJ, Cary, Manley), but has also loved the sound with Vitus.
My feeling is the Classe might be a bit lean for the Strads and not play to their strong suit (ie: midrange magic), whereas the Vitus would be more sympathetic to the Strads sound. Btw, rule of thumb: Vitus sounds best with Vitus. I (personally) wouldn’t match an RS-100 with a tube preamp or ss pre from another manufacturer as results could be a crap shoot. If you couldn’t afford to add a Vitus RL-101 or RD-100, you might want to consider an RI-100.
I own a Vitus SIA-025 which is warmer & more musical than the Reference series, though pricey. For the outlay, the Ref series is very good value paired with the right speakers.