Koetsu Blue Lace Onyx vs. Coralstone

The more expensive ones have a more refined sound. The lack of higher frequencies are not important, because the soft bass ability will be compensated with the improved midrange influence from the stone bodies.
The earthy feeling and sound of the Coralstone is special, it is a trip back into the History and I always did like the Blue Lace most with a Martini in my Hand - or some more - when listening to it. The longer I listened to it, the more I saw the "Gestalt" of tones.

.... the sound of the Koetsu Blue Lace Onyx is salubrious, exquisite, stunning, glorious and dazzling and the sound of the Koetsu Coralstone is superlative, smashing, magnificent, superb and impeccable...

Well, honestly, can't decide. They are both great ones. What amazes me all the time is that they are so much better than the wood bodies, it is hard to believe. A total different chapter from sonics. And both demand a serious metal Arm which has excellent energy transfer. When such one is used, they really come to life. When the System can do it, they sound like the real thing, not only with voices, with older classical records they create a holographic soundstage which is really unique. By far the best I ever listened to in the last 15 years. I compared them to the Lyras because I thought, the Lyras have probably a better detail but side by side they showed me that nothing is missing. Good as they are, but both, Blue Lace and Coralstone serve easily the same information AND more. Seriously a more of "being part of the recording", in a way, a superior view into the room (Vienna Sofiensaal for example)...in a way, I can FEEL the Ambience. Staggering.
Did not go for Diamond Cantilever, in a way I do not trust them, maybe others think different, but I prefer in a way "elastic" cantilever. Otherwise I use my cantileverless Ikeda System.

It is possible that I have auditioned Koetsu cartridges with not perfect setup ...

Indeed, that is really difficult based on the body which hides the view. You need an alignment System with a dimple that you know when it is done correctly. I have such alignment and even with that one I needed some time ...
Anyway, all I can say, these 2 Koetsus are so different to all other Koetsus I ever listened to that I think, that the Designer made probably some changes and did not communicate that. They are also VERY powerful in their gain, rated with 0.3mV, but I use much lower gain in my preamp than I do usually with carts of such output. Both they have a tremendous punch in the reproduction without any softness.