What I did:

1. authentication changed to Windows (PDC). After this all users and group accounts are available on NAS (-> connection to domain is working)

2. Created a share "Users" and added domain groups "domänen-admins", "domänen-benutzer" to the access list.

Now I can connect with "Administrator" account from a windows workstation.
But when using an other account, I get no access!
BTW: The other account is member of group "domänen-benutzer".

Please help me to use the NAS in windows domain network!