EvoTool works to change the X. I thing for M8+ bios you need version 1.0.9. I just flashed a m8_16 bios to a modchip on a 1.6 xbox and it works great. I edited this multi-bios with EvoTool and change the color of the X logo to blue. You can snag EvoTool from Xbins. If 1.0.9 doesn't work on a bios, then 1.0.7 will.