The problem is Logic Xpress does not work with BFD...
That simply isn't true, it's running fine here. Logic Express supports AU plug-ins, BFD is an AU plug-in. Having said that, modern computer systems are complex, especially when dealing with getting software from multiple vendors to work together, so there is a fair bit of scope for things to go wrong.
First - please confirm /exactly/ which version of OS X and Logic Express you are running.
Next, if you can go to /Library/Audio/Plug-Ins/Components, select one of the BFD components, and choose File -> Get Info from the Finder menu. If you post a screenshot of that info-box here, that will give us a good idea about whether the BFD AU is there and up-to-date.
Then, go to Applications, and run the BFD stand-alone app from there. If that runs correctly, again, that's a good indicator that things are mostly OK.
Let me know the outcome of those two things, and I can advise further.