[Bearxor]

As an old 6600 user, let me tell you what you can do.

You can unlock the Extended_ROM and load some apps in there. Basically, what that does is allow you to reinstall software after a hard reset automatically.

That's it!

No WM5 or WM6 upgrades are available for the PPC-6600.

Now, if you happen to have like an SX-66 or any other Blue Angel (not Harrier), then there is WM5 ROMs available at XDA-Dev.