et tu Koetsu?

Your description of the Koetsu sound is the most accurate I've read and mirrors my experience, including the Helikon. I am using a Urishi Vermillion with an Aesthetix Io dual chasis signature. As good as the Urishi is, I am considering the Onyx Platinum, but have heard that it is cold sounding and slightly bright and that the Rosewood Signature Platinum is smoother with more resolution than the Urishi and not as cool as the Onyx Platinum.
Perhaps you could contrast these three cartridges in your own eloquent style. Also, I am not aware of a Urishi Platinum.

My source tells me that the Urishi Platinum is not available at this time.

Extremephono,once again thanks for your eloquent description.
Verybigamp, if you only use the Onyx 2 % of the time, what is your mainstay cartridge? Also, in your experience, is the Koetsu Onyx Platinum elevated in the high frequencies?
When you say yellow, do you mean lacking resolution?