Nah didn't do that, but I installed the beta tool and runned without hardware check. It works OK now.

So, after soooo many problems I finally managed to make this rig work (I've got a few hashrate drops on some GPUs (30 to 25 very quickly) but it doesn't seem to affect the
hashrate at all and the rig looks stable, perhaps it's a bit too undervolted (90w)))!

Whoever wants to begin mining, I can only say one thing : Be prepared and never lose hope 

Thanks for the help !