Many people are underwhelmed with the sound of the MC275 because it has too little gain to sound its best with most preamps. Its 20 db gain is a full 9 or 10 db less than most amplifiers.
Get a tube preamp with higher than usual gain and you will be happy. I recommend the Cary Audio SLP 98 which has 20db gain, an awesome sounding preamp. The higher gain will give the 275 a shot of energy and wake it up with life like dynamics and drive.
I found this out with my 20db pass labs amp, it was a perfect match for my Cary SLP 05 preamp with 23 db gain. Low gain amps thrive on higher gain preamps.