Forgive me if I dont answer all your questions, my german is not so good.
I'll answer in English.
You are using a very old version of DSS5. I can not verify compatibility with 2008R2. You should upgrade to the latest version of DSS5, and consider even upgrading to DSS V6. and try authentication against 2008R2 again.
Also enable http share browsing in your NAS settings. This will allow https://xxx.xxx.xxx.xxx to work accordingly on port 444.