Thank you for your reply.
Brake set up:
I played with the brake controller to see if the trailer had enough (too much?) braking using the override function and I think the set up is ok.
It's also right in the middle of what the Tekonsha manual says is the range for the boost for my setup so I think the brake controller set up is ok.
The nose is a little high but not to the level that I would consider significant for the bubble in the level is still within the center marks (though it's closer to the one closer to the car)... May I be wrong on this?
I didn't do a running test with someone outside looking at it ... I think I'll have to do it if I can't find another explanation other than front wheels lock up.
About towing with the X5, yes I tow with it but I'll not comment for I don't want to start an endless argument.
Thank you again,