Edit: ok i get the same problem now after installing 17778 on my HTPC, and did some debugging.
The plugin is not being started at all, even though it reports correctly that the file being played is supported.
This means it's not related to asio4all, but looks like a problem in MP's plugin logic...
Funny thing is, when i make a build myself from the sourcecode, it works just fine
As soon as i know more I'll let you know.