Years ago when I owned Extremas, there was only one configuration that I tried that was truly magical...bi-amping them with a quartet of Naim NAP135 monoblocks, rated at 75watts. Using a single pair of the 135s resulted in a flat, lifeless sound. A Naim 250 sounded strangled. A pair of the very rare Exposure XVI (16) monoblocks was OK, but NOTHING like running them bi-amped.
The guy I sold them to came over to the house to pick them up and listened for a long, long time. He too had once owned the Extremas, sold them and was now desperately seeking a replacement pair (I should have taken this lesson and refused to sell them, as the Extremas are by far the single audio item I gave up that resulted in the most sellers regret). He said that he had never heard the Extremas sound anywhere as good as they did with the 4xNAP135s, and was planning to use them at home with a massive 750wpc set of VTL amps.
I heard from him two weeks later. When he hooked them up to the tubed VTLs they sounded nowhere as good as they had with my much lower powered, bi-amped solid state amps. He ended up selling them to a friend, as his expectations had been set listening to what they sounded like at my place.
If the MC275 are stereo, then by all means try biamping them....that has the potential to really make them sing. The brutal load of the woofer steals power and refinement from the more delicate needs of the tweeter, and having a dedicated tweeter amp is the way to go. This is of course for about any passive speaker, but seems to make a far bigger difference with the Extremas than with any other speakers I have tried passively bi-amping.
