Bi-amping a MC275 with my MC452.

I'm using a MC70 or c22 preamp same unit 

Interesting as i also have a 275 and 301 mono blocks i was considering doing the same.  one noted thing is the factory tubes Mac is using (JJ's) are ok modern sounding tubes but IMO are the weak link in the MC 275's performance so consider changing them asap. they are overly bright, lack musicality and are rather harsh sounding tubes. 

I know from experimenting that the SS mac amps have way better bass control and depth then the MC275. With the stock tubes the SS amps IMO have better top end as well, those JJ's are harsh sounding IMO. The midrange and sound staging is better on the tube amps though.

If you have a preamp like one of the current MAC ones you have the ability to adjust the gain on each output so matching would be easier. 

note sure if buying one to try is worth the money maybe a dealer would let you try it first. As for not working with horns that silly they are tube amps and horn's IMO always sound better with tubes, granted the amps have good tubes in them. maybe more power then needed but I'd say that for both amps your talking about. 

Interested to know how you fair. 

That’s exactly what I’m doing for music. The arc D 70 powers the mids and highs while the 462 powers the bass. I love the combo. Used with VSA vr 4 jr’s which have built in crossovers which makes biamping easy.

Added comment, I use a Schiit sys to balance the two amps which have different sensitivity.