I have owned both the 500MB's and the newer SA-500.1's.
In my system, I thought the older 500MB's sounded quite musical for the money, especially if purchased used. Mids and highs were nice and bass was a bit of a throwback, a little full and bloomy. Mine were a touch noisy but only in an absolute (they are not perfect) sense, not to the point of irritation or detraction from the music.
I did not particularly care for the newer SA-500.1's. Although Cary fixed the weaknesses of the 500MB's and made the newer amps quieter with improved bass damping and impact, did not IMO retain the level of musicality of the older 500MB's, particularly in the midrange where the newer amps sounded comparitively dry and sterile to me. I could live with the 500MB's but not with the newer model. My 2 cents.
