Good to see a european xi!! They are fairly rare in Europe, right? Probably more common in Norway than further south?
I believe the H&R coils actually use bilstein shocks. They are way too stiff for almost everyone who's tried them.
So what's wrong with your bilstein/eibach combo besides the fact that the rear shocks dont last? That gets the best reviews on here for lowered comfort on the xi. Bilsteins have a lifetime warranty- you should be getting free replacements.
That said- I do know of a few xi guys who blew out their rear bilsteins. It seems to have been a production issue with a batch of their shocks. I bet if you get a new set for the rear, they will last this time.
Did your xi come with the rough road package?