The Xenium will allow you to choose the BIOS you want to load in several different ways.
For example, you could configure it to boot an Xecuter 4980 Bios by pressing the A button on the controller, an Evox M7 bios by pressing, X, or an unmodified MS Bios to use with Xbox Live by holding Y.
Or, you can simply let it boot into the XeniumOS, and from there use the menu to choose which BIOS to load, or to disable the chip until the next reboot.
The idea behind this is that you won't NEED an external switch any more.
Understand now?
Flagg