Well, if you want the perspective of a previous McCormack amp owner, I'd say a tube preamp is mandatory, especially an Audible Illusions preamp. I've never heard the Y-S preamp, so can't comment on how that'd mate with McCormack.
Also, the McCormack can be further upgraded by the designer himself to sound even better (stock McCormack's are a tad bright and not so refined for my taste).
Also, the McCormack can be further upgraded by the designer himself to sound even better (stock McCormack's are a tad bright and not so refined for my taste).