Before you make a choice, ask yourself if this is your forever amp or not.  If it isn't, consider what the used McIntosh will be worth selling used compared to other equipment being offered?  Weather it is 2 years old or 20 years old you will get back something like 75% of what you bought it for. especially if it is in mint or VG condition.  There are few other brands but not the ones mentioned here that can come close to the Mac resale value.

Let me give you an example of my own personal experience, I bought a McIntosh MC152 power amp used for $2700, I sold it for $2500.00 in less than 3 hours posted here.  I had the first amp 3 years and sold it for only $200.00 less than I paid.  If I was selling it in today's market. I could have easily sold it for $3000.00

Mcintosh MC275 alternatives?

Look at the McIntosh MC2301 tube monoblock amps.

Mike

I'm not too familiar with tube designs, but would the Cary CAD-120S work?

Depending on speakers…. I wouldn’t rule out the Atma-Sphere M-60 or the Atma-Sphere Class D

Quicksilver “40 watt Mid Monos. Not pretty but no better amp available.”

Ugly amps need love too 

I have owned these amps since early 2015 .  They were only 13 months old when I got them.  I can not say enough good things about Quicksliver in general.  I have Mike’s Headphone amp and that is phenomenal too.  It’s built like a tank and super reliable like all Quicksilver amps    
 

I bought a new preamp last year and it really demonstrated how great they are  

Excellent value