Which Mc better Mid/High performance in BiAmp set up?

What preamp would you be driving these amps with? The reason I ask is that your MC7270 has an input impedance of only 20K, and many of the current generation McIntosh solid state amps have input impedances of 22K, or even 10K in some cases. Driving 20K and 22K or less at the same time would be a problem for some preamps, especially tube preamps. That would be true in many cases even if the preamp provides two sets of output jacks.

On the other hand, the 47K input impedance of the current version of the MC275 (assuming you would be using its unbalanced inputs), in combination with the 20K input impedance of your MC7270, would be much less likely to be a problem. Although some would say that doing so might compromise coherence between the mid/highs and the lows, given that one amp would be solid state and the other a very different tube-based design.

Regards,
-- Al

The C29 is rated to be able to drive a 10K load, so impedance matching would not be an issue if you chose one of the solid state McIntosh models having a 22K input impedance. Driving 22K and 20K in parallel corresponds to a load impedance that would be seen by the preamp of about 10.5K.

Personally, though, I agree with ZD. Rather than biamp, it would probably be better to just replace your present amp with one powerful recent generation solid state amp.

Good luck. Regards,
-- Al