Yamaha M series is unlike anything else they have ever built-in my opinion. The first 10% or so is Class "A" rated power. It is much warmer and smoother than most solid state gear (much more tube-like). I would compare it to threshold, sumo, aragon or other class A rated gear.
I believe there was an M-80,60,45 and maybe more. These amps also has multi-channel outputs with impedance matching built in. The M-80 could run up to 3 pairs.
Would I take it over older adcom? Without a doubt.
Would I take it over newer Adcom? Not sure.... Some newer adcom gear is quite nice but much more pricey than 20 year old Yamaha.
Listen for yourself.