McIntosh Guy Going Tubes? (Maybe?)

I agree with ^
Keep the 601s and get the C2600.
I have the C2500 with an MC 452 and the MEN 220. Very happy with this combination 

I put those same tubes in my C2500. Nice improvement 

If I were going to go to tubes I would trade in my MC452 and get the MC275. I doubt I will any time soon, because I like my 452. I’ve had tubes before (ARC) and they are great, but solid state tends to be more reliable and I like that. If you can, borrow a 275 from a Mac dealer and try it. It will sound different, and only you can decide if it floats your boat. Generally speaking, the tube amp will probably have a smoother top end and warmer, more refined midrange. Probably not as much bass, and won’t play as loud. Kinda depends on your speakers, I’m not familiar with yours. I would rather have your 601s, but that’s just me.

You will miss your 601s if you part with them. You have been warned!

I’m sure the C1100 is a step up from the C2600. 
C1100/MC601 combination would be awesome. I’m jealous.