Well I'm by far no expert, but what I did to make EB work with BI was to simply do this:

1.) copy your EB v.81 shortcut to some folder, say "My Documents".

2.) right click the shortcut and click "properties"

3.) a box should pop up with some text highlighted already. in this box, change the part where it says "C:\Program Files\Activision\Rome - Total War\RomeTW.exe" to "C:\Program Files\Activision\Rome - Total War\RomeTW-BI.exe". the only thing changed here is from RomeTW.exe to RomeTW-BI.exe. for me personally, i then renamed the shortcut, then sent it back to my desktop and EB with Bi works fine for me.

This will make EB run with BI...however I cant help with the custom battles or whatnot. :)