I have owned the Diablo 300 for a year and can tell you it was a very bad match for my Thiel CS 3.7 speakers.
If your speakers tend to be bright than don’t buy the Diablo 300 you will regret it as i did.
Vitus is much more musical, liquid sounding and has a lot of finesse as opposed to the Diablo 300.
Buy Gryphon only if your speakers are very smooth like Sonus Faber.
I now went the Vitus route with an SIA-025 Mk2 and am very happy.