Safari can't play application/x-mplayer2 sounds

I use Safari to visit websites that run Nagios, a network management system. When something
is wrong, Nagios displays web pages that have an imbedded object that's of MIME type
"application/x-mplayer2". Safari displays a pop-up that says

Safari cannot find the Internet plug-in.

The page "Nagios" has a content of MIME type
"application/x-mplayer2". Because you don't have a
plug-in installed for this MIME type, this content
can't be displayed.

I can navigate directly to file .wav file and Safari (QuickTime?) plays the sound. I think
I need to get "application/x-mplayer2" added to the list of MIME types that the QuickTime
plug-in handles. Is there a way to do that?

I know that QuickTime has a System Preferences pane, with an "Advanced" tab with a
"MIME Settings" button. That doesn't help - it controls MIME types that QuickTime supports,
not the MIME types that the QuickTime plug-in supports.

Also, I had Window Media Player installed, but it gave "One or more arguments are not valid".