100W+ solid-state amps known for beautiful mids

If you can get a 200W+ amp, get it.
the headroom you will need.

Bakoon amplfiers have the most pure,detailed and natural sounding midrange I have heard.They sound neither warm nor cold and when you hear them aspects like that become irrelevant because they just sound right.They used to make 100 watt monoblocks but I am not sure that they do any more and they are not about power anyway.They are about clarity and finesse.They sound a bit like the Dartzeel but with even more immediacy, clarity and vibrancy although perhaps not quite as good bass.They also require more careful speaker matching and are much better driving 8 ohms than 4.

If you can get a 200W+ amp, get it.
the headroom you will need.

Buying based on watts is not a good formula. 

Like someone else mentioned, I have Keith Herron's M1 monoblocks.  They are "only" 150 watts each, but they have a very large toroidal transformer that provides all the headroom I need.  Previously I had Rogue Audio M180 tubed monoblocks (which I loved), but the M1's provide all the power I need and are cleaner and more detailed than the M180s.

If my budget allowed, I'd be more than happy with a 100 WPC darTZeel amp.  Some of the best midrange I've heard came from a 48 WPC Line Magnetic 805iA integrated powering Harbeth 40.1 speakers.  Having plenty of power certainly can help in the right design, but there's so much more to an amp than how many watts it puts out.

I searched long and hard to find an amplifier that sounded good with my Martin Logan CLS IIz. After trying numerous high-end tube and solid-state amplifiers I settled on the Classe CA-200.

@peguinpower. I had the exact opposite experience with the Pass X150.8 and Audio Research.  I found the ARC to have wonderful mids and the Pass very sterile lacking any midrange magic.  Could be system dependent but it's crazy how we have totally different experiences.