Focal 1028+Mcintosh MC275

I have heard both those pieces but not together. You should be fine to run them together. Probably will sound nice. 
Last time I heard the MC275 was on a pair of B&W 805D3 and it did a good job of taming the highs. 

I wouldn't hesitate to own an MC 275 MKV again.

You absolutely cannot go wrong with the MC275. It has plenty of power and it is so smooth. 

The dealer I purchased my MC275 and La Scala speakers from is also a Focal dealer. They were primarily using McIntosh SS amps with tube Pre-amps all the Focal speakers. I did see a MC275 hooked up to a pair of Focals, but unfortunately didn't get to hear the combination. 

I do admit that I was probably too distracted staring at the pair of Sonus Faber SE speakers in the next room. It's not often I get to see a pair of $250,000 speakers. He did let me listen to a pair of Sonus Faber Aida's though. That was really really nice. 

Cheers!

I have a McIntosh MC452 driving a pair of Focal Sopra No2's and that combination works really well.  I've auditioned my speakers with other amplifiers and have found too many of them cause "edginess" with that Focal tweeter, but not the McIntosh.  If anything, the MC275 tube amp should pair as well, if not better than the amp I own.

I'd say "go for it"!