In this well descripted analysis, Markus Gaasedelen has managed to successfully dump the console's secret boot ROM by intercepting the Intel CPU's JTAG functionality with a custom made adapter. Its amazing to see discoveries appear here and there to this very day in 2023, since this can open the full capabilities of the hardware to many hobbyists and hardcore developers.
Detailed explanation can be found here: https://blog.ret2.io/2023/08/09/jtag-hacking-the-original-xbox-2023/