He fired up Xemu with a debugger attached. As the emulator started, he froze the execution at the very first cycle. There it was. The MCPX Boot ROM mapping itself to physical address 0xFFFF0000 . The CPU, lost and directionless, would jump to that address on reset.
is a low-level, full-system emulator. This means it doesn't just mimic the games; it recreates the actual hardware of the 2001 Microsoft console.
In Xemu, a popular open-source low-level emulator, the user must supply a legally dumped mcpx.bin image. Without it, Xemu cannot progress past the “boot ROM” phase.