Argento cables - any experience?

Fla, that is an interesting question. Evaluting US retail prices, the Piano Diacera represents an 80% additional price premium over the Piano Cera. Is it better? Of course! Is the improvement commensurate with the premium? Of course not, and this is probably the answer you would get from Tidal. The diamond tweeter upgrade probably makes sense for the Contriva but not for the Piano.

I have only listened the Sunray and the diamond tweeter is out of this world. But I believe that the Cera is better value for money and you can always upgrade it to a Diacera later...

Geopolitis, I have only heard Tidal speakers with the diamond tweeter. I have long loved the plasma tweeter used in Acapella products but generally it sticks out as superior to and different from the other drivers. All that I can really say is that the diamond tweeter in Tidals sounds every bit as good as the plasma, but different, and it is seamlessly integrated with the other drivers.

How good are the old ARGENTO SERENITY REFERENCE 2MTR speaker cables?

Very very good. In my system it was almost impossible to distinguish between a Stealth Indra and an
old Argento Reference interconnect with the Eichmann bullets termination