Well here is a factor that may drive your decision. ARC is now charging $275 per tube for matched KT-150s. I surmise that the Ref 250SE runs twice as many KT-150s as compared to the Ref 160M. If so, … do the math and think how much tube replacement will cost you after 3000 hours of play time.
BTW, if you are thinking that the cost of tube replacement can be reduced by going to 3rd party tube vendors, think about this. I purchased replacement matched KT-150s from a well respected tube vendor several years ago, ... before ARC upgraded my Ref 150 to the SE version. No names mentioned. The bias spread was barely within ARC spec. Fortunately, the SE upgrade came with fresh ARC KT-150s. So the old batch of KT-150s are in back-up reserve.
And perhaps that is another reason to think about the Ref 160M. Unlike earlier ARC Ref amps, I understand the Ref 160M (and S) has an auto bias feature. Not sure, but I think the Ref 160M (and S) may (??) also have an electronic circuit breaker in case a tube arcs. Check that out too. More to think about.
No comment about SQ. Never heard the Ref 250SE or Ref 160 M (or S). I own the Ref 150 SE, which I love. But I am at the 2000 hour mark on my KT-150s and thinking about tube replacement. I am working on a possible work-around with my spare batch of KT-150s. If my idea works out, I'll report back.
BIF