First COPY your Evolution-X dashboard from xboxdash.xbe to yboxdash.xbe and place it on the Xbox's C:\ drive.
Then flash the bios with the ybox bios.
Reboot, and your system should still come up in Evolution-X.
Now ftp to it again and rename the original M-I-C-R-O-S-O-F-T dash to xboxdash.xbe
Modify the evox.ini file to reflect this change (msxboxdash.xbe ==> xboxdash.xbe) and maybe even xbmp's config file.
Reboot the Xbox again.
Make sure you can drop to the dash from Evolution-X.
If so insert the NEW XboxLive cd, and let it boot.
it will "update" your dashboard. When it's done it will shutdown your machine.
Eject the disk.
The Xbox will come back up in Evolution-X, drop to the MSdashboard.
Now you'll see a new tab that says XBOX Live in the MS dash.
Reboot again.
If you want you can find the livelogo.wma file (or whatever it's called) and rename it's suffix. That way no more annoying transition logo.
Your work is done.
No more XboxLive worries.