Well it would really suck if this can't be done. I am switching from vB4 to XenForo and that editor is one great think vB has...
I wouldn't worry so much about it if it wasn't for the hundreds of threads and posts my forum has which were formatted using CKEditor..
The editor wouldn't make the slightest bit of difference to your problem.
An editor is simply that: a method of text input and other controls. All those controls do (e.g. the editor buttons) is just input text. It has nothing to do with how the post is then formatted, or how the code is interpreted.
You don't need a new editor. As oman says, you need the equivalent BB Code added to XenForo which can be done via existing add-ons or using the built in Custom BB Code system.