Compared Diamond and Callisto 1:1 few years ago, think it was one of the Callisto's earliest release...
Callisto won with classic knock-out in first round.
Yesterday I tried Callisto with Intona USB 2.0 High-Speed isolator - https://6moons.com/audioreviews2/intona/1.html
Result was similar, but in this case, there was literally no result at all - neither good, nor bad.
But...I tried another USB cable, diy, from my friend...and in this case sound...
Few words about Callisto...
First of all, like Goran, I also know FTA designer and agreed about everything Goran wrote about him. Modest, willing to share hugh knowledge and experience.
Personaly, I used many FTA cables in many years, but Callisto is something quite different, best USB he ever...