MCPX

The MCPX is the southbridge chip of the Xbox chipset by Nvidia. It contains the sound processors (APU and ACI) and also the USB, PCI, IDE, etc, controllers[1], [2].

The MCPX is also the home to the secret MCPX ROM.

And it's also the home of the famous PC Speaker Signal.
One just has to solder a Speaker on (MXPC pin L21) and it can be used just like on the PC.
For some test code see https://github.com/0DaveX/beep/