To use a car analogy, powerful SS amps have a very rough engine idle speed, like a race car, while tube amps idle like a Lexus. Unfortunately, SS powerful amps will work in the "rough-idle", high crossover distortion region with high efficiency speakers.
I am not familiar with the MC2500. My Mc402 sounded smooth from the first Watt up, though I could still hear a slight veiling/graininess at very very low late night listening levels.
You may want to make a simple test: play a good recording with piano, vocals and cymbals late at night, at a very low level, say 400mW on the Mac VUs and listen close to your current speakers. 400 mW was the average level I used to drive my high-efficiency ZU Druid speakers with an Mc402. The sound pressure level in-room was about 90 db, pretty high, so you see there is a method to my madness!
If you hear any graininess/veiling during this test, as compared to normal listening levels, I believe you would be happier with a tube amp or a class A solid state amp (e.g Pass Labs) driving hi-eff speakers.
My personal amp history may help explain my POV:
BEL 1001 (50 Watts/channel)
Gamut D200 (200 Watts)
Mc402 (400 Watts)
ASR Emmiter II (500 Watts)
have you noticed the power race trend? They all sounde fine, but something wasmissing.
happiness with an 845 20W SET amp and 90 db efficiency / 8 ohm speakers.
SETs plus hi-eff speakers have a special mojo, a magical midrange, clean highs, great soundstaging and excellent inner dynamics. What they do best is not easy to describe in Hi-Fi terms, though easier to describe in musical terms: there is more emotion in the air.
If you want your music really loud, look for speakers with 96 db/watt or higher efficiency and a smooth impedance curve around 8 ohms.