There isn't a PC speaker header! The Front Panel Audio Header (AUDIO1) is for the front panel mic and sound-out sockets; you can attach your headphones or external speakers to this. For external speakers, it's probably neater to attach them to the line-out (green-rimmed) connector on the rear IO panel.
But I don't see a PC Speaker connector there at all. Maybe it has an onboard speaker?
Are you concerned with your external speakers or the PC speaker that is mostly used for beep codes?