Are you trying to set up xemu, or are you looking for the specific tools to dump the ROM from your own hardware?
To get it legally, you must "dump" it from your own physical Xbox hardware. 🛠️ Requirements A (softmodded or hardmodded).
You can extract the ROM from a physical Xbox console using tools like mcpx-attack or by hex-editing a dumped BIOS image. Open-Source Alternatives: Projects like Fancy Mouse Boot ROM