How to associate multimedia keys to Foobar2000?
Solution 1:
For Play/Pause:
File -> Preferences -> General -> Keyboard Shortcuts
Click Add New and setup the binding you want. Make sure to select Global Hotkey.
As for launching from a keystroke, when you edit the properties of a shortcut you can assign a Shortcut key.
Solution 2:
Multimedia keyboards + foobar2000: A complete guide detailed everything that I wanted to do with the keyboard.