This is for the DCS-932LB1 but should work on others. Add the below to your reverse proxy configuration:

ProxyPreserveHost On # fixes digest authentication
RequestHeader set User-Agent "Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 7.0; InfoPath.3; .NET CLR 3.1.40767; Trident/6.0; en-IN)" # Interface requires IE

By doing this you can allow different browsers (Chrome, Firefox, etc) to access the web GUI as it fakes the User-Agent.