Xemu does not distribute BIOS files. You must dump them from hardware you own. No BIOS = no emulation.
Because xemu is a low-level emulator, it doesn't "fake" the Xbox environment; it actually emulates the hardware. To do this, you must provide four essential files:
Via command line:
Once you have your files, configuring the emulator is a straightforward process: YouTube·UrCasualGamer Xbox Emulator Xemu Setup Guide
Here’s a draft you can use for a page, guide, or README section about — the required original Microsoft Xbox BIOS files for the Xemu emulator.