Thanks for the tip. I forgot to mention that I'm also using MiniDLNA server. No big differences in multicasts, except they come slightly different order and this line

NT:urn:microsoft.com:service:X_MS_MediaReceiverReg istrar:1

Changing that line did not help.

However, I noticed that Zhaan is key. If Zhaan is not running, Mediabox don't discover server. As soon as Zhaan is running, both Mediabox and Zhaan find server, Media player don't. Zhaans seems to duplicate the multicast messages that ssdp-fake is creating (and ssdp-fake ignores them).

Maybe Zhaan is doing also something else besides multicasting. Oh well, I'm glad I get at least the Mediabox running with ssdp-fake and Zhaan.