Well, if you insist, quick thumbnails, as audio prose is not my specialty.
The Lyra Helikon was my reference for about 18 months, and I was very happy with it. After living with the other 'mellow' cartridges, the Lyra's transparency, air and spaciousness were very welcome. It could sound lean at times though. Great recordings sounded great, weaker recordings sounded, well weaker.
The Koetsu Rosewood Signature was a very sweet cartridge, lovely bloom, rich vocals, though a bit soft in the high's. It erred on the warm side of neutral. Never offensive, but lacking in resolution.
The Cardas Heart was very similar to the Koetsu. Always easy on the ears, but lacking in resolution.
The Benz, I owned a Glider and a Ruby 2, were similar in sonic signature, though I never really grew to like either of them. I know the Cardas is based on the Ruby, but the Heart had more life. The Benz cartridges seemed to have some mid-upper bass bloat that smeared detail in the midrange, and just didn't sound natural to me. I don't know what Cardas did, but the bass seemed to tighten up enough that the midrange was clearer than with the Ruby.
Dynavector, I owned the 10X4 mk II, and the 20XH. The Dynavector's are really good cartridge's as well. They seem to have a nice balance between the warmth of the Koetsu/Cardas/Benz cart's and the life of the Lyra. Dynamic, powerful, yet no glare or offense. Very good 'bang for the buck' line, I would love to hear their top end DRT-XV-1s one day. If the ZYX has a natural competitor, it could be the Dynevector's.
Which I guess brings me to the ZYX. I first bought the Airy 3 S-SB about 18 months ago, when the Lyra Helikon was my reference. I was immediately stunned by the natural presentation and size of the stage. Timbre's and tonal accuracy just sounded so real it was almost frightnening. 'Right' and 'Natural' are the words that kept popping into my head. Not lean, not sweet, just right. It is very hard to describe, but easy to understand when something (to steal conrad-johnson's line) "just sounds right". Nothing was forced or artificial sounding, no glare, yet no information was missing. Not warm sounding, but 'relaxed'. It's not something that you have to strain to hear either. I sat there for a week with a stupid grin on my face (alright, maybe that's natural).
Anyway, I was apprehensive about trying the UNIverse. It was a big step up money wise, twice the price in fact. I was wondering 'how much better could it get'? Well curiousity got the best of me, and after a couple months with the Airy 3 I bit the bullet and went for a UNIverse S-SB. It was better all around. Actually describing sonic details seems to be a mute point, as in the last 15 months all I've done is listen to music now. No longer do I hear warmth or leaness, no air or rolled off high's, no more listening to bass definition or midrange anomolies. No longer do I listen for a 'good or bad' recording. Now I just listen to the music. It's so natural, so right, that I don't try to dissect the music anymore. I simply enjoy.
Is the UNIverse worth twice the price of the Airy 3? That's a tough question to answer, and would depend on your financial situation. It is definitely better than the Airy 3, but the Airy 3 will get you 85-90% of the way there for 50% of the price.
The highest praise that I can give the UNIverse is that I've owned it for 15 months now and have absolutely no audio itch whatsoever to try anything else. That is saying a lot for someone who doesn't own a single piece of equipment that's over two years old. It's rare that something satisfies me to the extent that the UNIverse has. If only I could find more gear like it, I may just step off this merry-go-round for good. :)
Hopefully this helps clarify my journey somewhat, and answers any of your questions.
Regards,
John