There’s nothing more to do, the verbiage in Messenger is only because the only plugin Microsoft ever produced themselves was for WMP. The toggle applies to any client adds support.
The way this works isn’t complicated, players send the song information via a standard window message to Messenger. The only thing that causes problems is that the format changed from MSN Messenger to Windows Live Messenger, so not all Messenger versions are compatible with all plugin versions.
I just installed the latest Winamp, the plugin, Messenger 8.1, enabled the option in Messenger, and it all worked out of the box without any further configuration.