Can you give your impressions of the M100 and what speakers you're using with them? I am considering buying a pair to use with a Levinson 380S preamp.
I like the BAT running true balance into Clayton. I have used the BAT VK5, or if budget permits, BAT VK30SE or VK50SE. The Clayton is neutral enough to work fine with any preamp, but go with a true balanced preamp design. Spectral DMC20 would be good too (but Mr. Spectral will shoot me for recommending his preamp on non Spectral system). ML preamp, Proceed, or older Krell such as KBL all works fine.
However, old school tube pre like Conrad Johnson PV8, ARC SP6, Marantz 7 or Mcintosh C22 will be too slow and short in extension and takes the life away from Clayton.
BTW, I have not known of better sounding amps like Clayton M100 under $10K new, hope I had the money to try bigger S2000.