Worthy upgrade?

I agree your speakers are deserving of better amplification. A Gryphon Diablo 300 will give you comparable dynamics without the detail-obscuring overt warmth. 

I had heimdall 2 cables when I owned SF Serafinos. Tried more expensive nordhost cables and Audioquest. Any difference I heard was negligible and not necessarily better. That’s just to my ears- many hear a “night and day” difference in cables, but my experience is that the differences are subtle. 

I would move away from a McIntosh integrated. Your speakers are great and although McIntosh and Sonus Faber generally sound good together I think you are missing the benefots of a separate amp and pre amp.  I had a McIntosh set up and moved away from it to tubes (Audio Research Ref160S and Ref6SE) and this was an astonishing improvement in overall sound quality.  I think you might need more detail for those speakers.  I have since moved to SS but your system deserves a better amp and pre amp.  Let us know how you make out.

I heard a significant improvement in the sound. But, is the upgrade ridiculous in terms of the rest of my system?
 

Given that the goal of an upgrade is to improve one’s system, if you can afford it, I don’t see why not. You already heard “significant” improvement. The only question I would have is: could I spend less money somewhere else in the system and obtain better performance? Keep in mind that the rest of your system will most likely change too overtime. That’s the nature of the game. My 2 cents: significant improvements are not usually easy to come, thread wisely. 

My 2 cents..The MacIntosh is your weakest link. Restaurants that make everything generally don’t do it all very well, separates is the way to go. Trying to prop up Mid-Fi with wires is subjective and can be an expensive rabbit hole. 
Cheers