Polymer - amazing above the two 6" drivers. They would be a top contender if the base was better. Slightly lose, lack true impact, and just not up to the rest of that amazing speaker. A shame, because if they had a larger low end driver cabinet with more punch and extension they would be world class!!! The top 3 drivers ok that narrow baffle design are just magic though. So if your not looking for that low extension punch and imaging and proper tonality are of utmost importance then the MKs-X is a huge performer!!
Zellaton - wonderful speaker but same low frequency weaknesses in my opinion. For jazz, small orchestral, vocals, quartet, etc they are fast fast fast, accurate, musical and accurate. I was not engaged once during my listening session and the low frequency paucity turned me off. Again, more a matter of taste then quality.
Vivid - another great speaker but just never grabbed me in the right way. The non-nautilus design has a lot of rear firing drivers and needs a ton of space out into the room, and the nautilus design did everything well but never really wisped me away, to that lost in the music moment.
YG - truly a masterful creation. They do everything really well and nothing lacking. If my room were longer it would be in my top contenders. Imaging, impact, tone, dynamics, subtlety, engaging? All there. But if you look at the actual design of the speaker, they require you to sit far enough away to allow those drivers to properly integrate. And I felt that I couldn't get that distance in my room. More a decision of practicality then performance. That Sonja is a true statement product though. No doubt.
If the Kawero didn't have that brightness issue and I had a bigger room they would be an absolute top contender. Vivid & Zellaton no thanks, personal opinion. Polymer would be a joke run with better low end and YG are awesome but, I think, needed a longer room then I have.