Lycan,
I was having issues streaming audio with the DIR-615_B. The router log would show the following error when I tried to stream audio with Windows Media Player:
RTSP ALG rejected packet from <ip address & port of streaming music> to <my wan ip address and port>
I was able to fix the issue by unchecking the RTSP ALG in Firewall settings in the D-Link router. The only other way to resolve the problem was to uncheck RTSP/TCP in Tools->Options->Network tab of Windows Media Player.
Thank you for looking into this issue.
Sincerely,
SurfingR