Sanity check on new system?

I agree with noromance. These are fairly safe bets all around, but might not have the best synergy. If you want headbanging volume levels, you might be better off with a more powerful amplifier, maybe something with KT120 tubes. On the plus side, all these brands hold their value rather well.

If it really is to be your first system, I think you’ll be blown away by the sound. You could do a lot worse.

I haven't heard the 803s, but from everything I've read, it seems they perform best with high power. My KT88 Cayin amp was modeled after the MC275 and has similar power. I don't think I'd want to pair it with B&W 803s, but if you already own the 275, won't hurt to try it. 

It's best if you can manage to audition gear somewhere, especially speakers, as they will have the greatest influence on your system's performance. You might discover you don't like B&W.