Marco, it's stated everywhere that ZYX distributors and Nakatsuka-San support only models with real serial numbers (no support for grey market products like those from ebay in hong kong). If you have cartridges from official ZYX distributors they can take care of it (in case of retip/service questions). ZYX retip policy is interesting, they do not retip old cartridge, they will supply brand new cartridge with new serial number to customers (if you old original is broken). So the cartridge with broken tip must be returned to ZYX in Japan for replacement. It's not cheap, but you pay less for new one - this is what they call retip. If you have no distributor in Italy you can contact Mehran @ SoraSound in USA (he's a top guy in business).
If you preffer retipping old cartridge then Sound Smith can do that for reasonable price, no problem. But it will be no longer ZYX home sound! And if some other vendor has touched original zyx you will no longer get Nakatsuka-san support.
I've had some distortion problems in the right channel with new gray market Airy in the beggining, later the problem dissapeared, maybe it was just burn-in period.
Preamp is very important for cartridges like ZYX, it was a big improvement to use ZYX CPP-1 Pre-Pre (instead of my existing MC stage) and MM stage.
