In Your example the page offers mimetype: application/x-mplayer2
( which can be played with media player - but with some other players too )
The message = from default nullplugin (npnul32.dll // "npdefpluginpro.dll" is better)
& means that the needed plugin or applicaton is not found and listed in about:plugins
You can test how new k-m reacts to differnt codes calling music plugin:
http://home.htp-tel.de/sterntaler/test.html#plugins
If You read German a little the link will give You a list of mimetypes:
http://en.selfhtml.org/diverses/mimetypen.htm
New 0.9.12 and 1.0b test versions both can use Your Windows Media player
if active x support is activated or installed and activated respectively.
You can influence which player is used for a mimtype via Mtypes by Monkee-Sage.
How far is You newest skin project ? Greetings to Sweden