To help give you the most accurate advice for your setup, let me know: Which are you planning to use? Do you currently own a physical Original Xbox console ?
The MCPX code initializes the graphics chip (NV2A) and the system RAM. Download Mcpx Boot Rom Image
If your file matches this MD5 hash, you have a perfect, uncorrupted copy of the Xbox MCPX Boot ROM. How to Configure the MCPX Image in xemu To help give you the most accurate advice