Update: I found someone who offers to upgrade my analog Cluster to the new digital one (6WB) for 1000€,- in total and I am going to do it.
Its an local BMW tuner like Bimmertech.
http://www.bimmerretrofit.at
Although he is 300km away I am going to drive there cause then it's a 100% sure thing. I can watch him installing it and he will give me tipps. He is specialized in upgrading all BMW Multimedia systems with original BMW parts. He has many customers who ordered an BMW with small screens and without navi or bluetooth and he upgrades them as if BMW would do it!
He also mentioned you need to keep the old cluster cause if BMW decides to call you car for a unscheduled maintenance you need to have the old one and original cluster installed. He also told me that the info for the cluster is saved on the cluster itself so whenever I switch them I dont need to code them again!
So far he gave me reall good info I would say.
Ill update as soon as the Android-Multimedia system is here. In 2 weeks Ill upgrade my X3 with an high-end hifi-system for about 1500€,- aswell.
I found a company that won 7 years in a row the national car-hifi-contest and I think they are a good choice aswell.
Let me know if someone here is going to order the 6WB online.
-Thanks