Hello Philipp,
we also had a virtual appliance and authenticate the user with LDAP against the active Directory. Authenticate Domain users, when Domain users is Primary Group in the AD is a Little bit tricky. you have to use a ldap browser and look for the Primary Group id in the Active Directory for Domain users. you can find this under "objectSid" and you Need the last numbers behind the last Hyphen. at last you have to create a new authorization Group in Netsight and give the Membership criteria "primaryGroupID=xxxx". Of course you have to set your ldap configuration at first!