As far as I know, the latest drivers for the Microsoft Sidewinder X4 Keyboard only function with Windows Media Player. I use Nightingale to manage my music so it was either me or keyboard that was going to have to adapt. At first, I installed a plugin for “command-line” support so I could run bind the media keys to shortcuts with command-line switches, but that would always cause the program that I was currently in to lose focus. That wasn’t normally a problem unless I was in some sort of full-screen application, especially ones with 3D environments like Max Payne 3.
Many Google searches later after looking for a new solution, I stumbled about someone’s neat little program called MediaKeys. There’s probably a lot of programs called that, but this one is really different because all it does is fire off standard media keys that most programs accept. Nightingale picks up on it when told to pick up on them, so I found it really handy. Hit the link to find out how to set it up with the Sidewinder X4 and probably the Sidewinder X6 as well.
EDIT: Alternatively, you can kill the “itype.exe” process or better known as Intellitype (Pro). It would seem as though that Intellitype (Pro)’s media keys only send codes that only Windows Media Player accepts, while with it off, the keyboard fires off regular media keys that recognizable to most media players.