Thanks Ikarasu for your support ^^
Well I have stepped up the tone a bit in my mails and I got to say that it worked (they answered in like 4 hours). They still think that it's a software problem. They insist on the fact that I might have setup the software incorrectly. That's just nonesense.
WhiteRIP costs 900$ and is able to print anything I ask it to it. The details and precision of every prints of that RIP are astonishing. It's even better than the AcroRip when I got it in the first days. The resolution in WhiteRIP though is still under 5760x1440 but quality wise it's worth the money.
On the other hand, Acrorip is slowly getting useless as the 1440 x 1440 prints are OK 1 time out of 7 prints (smears starting to apprear, unprecise print, a bit blurry etc..)
The more I print with AcroRip, the more the prints are bad.
So I'm thinking about this theory : If you buy the printer alone and use any kind of free software or the one they include, then you've done half the job. Because for now all I know is that the RIP choice is as crucial as the printer choice. This .. I didn't knew it.
So i'm about to buy some decent RIP software. I'm thinking about WhiteRIP for now.
Tell them you want the firmware and eeprom as a last ditch effort to fix it, before you Skip for a refund / do a charge back.
If it's a one of a printer, I wouldn't install the official firmware for said printer. Odds are they're using a modified one to get around protections... This is also probably what's causing your printing issues. If the firmware has protection, and you install it on a clone.. odds are you'll brick the printer.
I have already updated the firmare to the latest version and already rewrote the EEPROM with many L800 eeprom versions I could find on the web (but I put my original backup file in the printer at the end so no risk here) For now it's working good , but i'll do it. I'll ask them those original files again just In case I have another type of problem later..
The drawback is impossible btw. There are no guaratee and no returns possible with this product or any product of the WayPrinter company.
It was a risk since the beginning .. And after all these problems, I have to say that I have learned a lot so far.. a lot more than I wanted to but hey ... at least I know how my machine works a tight more now