The M8 bios is a hacked bios made by the Evox team.
I assume you're using a kernel patcher such as nkpatcher rather than a bios loader (which were very common before kernel patchers came to be as good as they are now).
A bios loader requires a bios file to load, and Evox M8Plus is the bios of choice (necessity really) for softmodders working with 1.6/1.6b Xboxes.
Kernel patchers just patch the retail kernel (re: bios) and thus don't require a separate bios file like M8 or an Xecuter bios. You're good, and well set up.
Read this for full info on loaders/patchers:
http://forums.xbox-scene.com/index.php?showtopic=320590