Are you sure about the tube compliment? I thought the m60 used four EL34 tubes? Also the m60 has solid state rectification, whereas the Silver monos use a tube rectifier. I had a pair of Silver Mono's for about a year and did enjoy them very much. They are a pentode design so would be emphasizing the bass a bit more, boosted yet further by the use of KT88's vs EL34's (assuming I am correct there). As far as midrange magic goes, pentode is not considered the best where that's concerned. My Silver monos have been bested in that regard by other triode and push/pull designs I've used (Mini-Mites, EL34 Triodes, and 300B SET). But do phone up Mike Sanders and ask....he's easier to reach by phone than by email and tends to be very brief in his email responses. I'm sure he would give you a candid assessment of his view of the differences in the two designs.
Marco
Marco