Serviio

I'm using a Win2003 SBS server and the Serviio software. Through DLNA I can play my music on my Onkyo TX-NR515 from my server. I also can use the webinterface to browse and play the music.

I added a NAT rule in my modem and can access via the webbrowser my music. Is it possible to play the music using Windows Media Player or Winamp or perhaps some other mediaplayer?

Not really, it's server using Serviio API. You would have to use the API to, for example, generate WinAmp playlists - then it would work.