have demoed the Olympica III and Nova 3 a few times. I own the Revel 228be and use subs which is important I think.
The short version is I think the Revels are a better speaker.
The long version… the Sonus Fabers have a slight dip in the upper mids. 2-3 db in the 2-3k range but I think the highs are a bit more tipped up at 10k compared to the revels. The Sonus Fabers also have a bit rounder bass with a bit of upper bass bloom.
I have not heard the Kanta so I can’t comment but based on their measurements they are a touch bright. Depending on your age (upper hearing) it could be a good or bad thing.
Personally I would not by focal or Sonus Faber as a second set of speakers to revel. They are both a step down in absolutes and just different. You might like different better though. If I were going to try something different I would try open baffle or horns for a major change.