I had an L1/X1 (with an A1.5 amp) in my system prior to getting my MSB Reference. I ended up selling it and added the Reference Digital Director which did make a positive impact in my system. I also sold the A1.5 and replaced it with a D'Agostino Momentum MxV S250. In my room, these moves sound...
I have heard the Extreme w/the Taiko switch in my own system and preferred the Antipodes K50 G3 to it. The OLADRA G4 is even better than the K50. I know that you didn't mention Antipodes, but you may want to check them out if you haven't already.
The Everest is better than the Denali, but if you add a Typhon T2 to the Denali, the pair is as good as, if not better, than the Everest. And, no, you can't add a T2 to an Everest (per Shunyata).
FWIW, I have my subs plugged into my Denali 6000 v2 and my amp is the only thing plugged into the T2. I haven't noticed any ill effects having it set up this way. My front end is on a different wall and connected to an Everest.