Hi Ralph,
Actually I had success with tube and solid state preamps with the M-100's. I would avoid tube preamps with high output impedence like CJ's though (700 ohms). Tube pre's with output impedence at or below 300 ohms, like BAT worked as well or better with the M-100's than the solid state preamps from Threshold/Krell/Mark Levinson that I tried with them.
John