My X5 has the factory tow hitch, but I hear Execuhitch (or something like that) might allow you to keep your existing bumper.
THe Tekonsha RF brake controller is a good unit, but you will need a domestic truck to plug in when you try to pair it to the controller, and there are threads out there about how to do that.
You will also probably need to code the X5 to add a towing module. Mine had the factory package, and yet I couldn't figure out why i was getting a bulb out indicator when I'd connect the trailer...it turned out I didn';t even have the module coded, so I had to add it. Go to bmwcoding.com and search for towing info for details.
Good luck / happy towing!