Zorro-
I have had the following McIntosh SS amps,
MC150
MC300
MC501 (monos)
MC601 (like yours)
I was a Mac guy for years until I bought the Pass XA60.8, then the XA 100.8, and then the XA 160.8. Once I heard what Pass did better than Mac (which is most things), all my Mac gear went on the block. Pass amps are more articulate and transparent without being bright, and throw a wider soundstage with better separation of instruments. I am certain you will find the same. Note that now I have a Coda Model 16 and enjoy my system even more. Do not even bother with Pass preamps, however...they are anemic and soul-less beyond describe. Odd, I know.
Good luck and happy listening!