Getting music server in network properly

My music server (Hifidelio 400 Pro) is connected to the network via WLAN,
and it communicates with a router (Sitecom WL-154) somewhere in the house.

A PC (XP Home), Laptop (XP Home) and Mac Pro (Leopard) are in the network as
well, via wired LAN.

The music server has to play music directly from the PC, Laptop and Mac.
It does play music from the Laptop, but doesn't from the PC or the Mac.

The music-server's display shows the PC and the Mac, but can't communicatie.

My Mac is rather new, I have to find out later on to run it properly.
But the PC has to communicate with the music-server. That's important for me.

What can I do. Please help me.

Thanks in advance. PR