According to the KB Article 2796618 “Windows 8 introduced a number of significant infrastructure changes on which extenders for Windows Media Center relied. These include changes to the RDP protocol. Because of these necessary changes, extender devices that were designed for Windows XP, Windows Vista, or Windows 7 cannot connect to Windows 8 Media Center PCs. These devices should still work with earlier versions of Windows.”
As per this KB Article XBox 360 is the only supported extender in Windows 8 Media Center PC. Third-party extenders that work with earlier versions of Windows won’t work with Windows 8.