Yeah it kinda sucks with the facelifted X's. Not only does the whole 4.8is bumper costs more then the underbumper of the 4.6is. It means more pieces need to be painted, which equals to more money. And it also takes more time, the 4.6is underbumper you can just glue on, but the 4.8is, you have to remove the whole facelifted bumper.
Although the underbumpers of both the prefacelift and facelifted X's look similar, it has been said the 4.6is underbumper wont fit under the facelifted ones. I hope this doesn't confuse you... Sorry if it does.
Here's a link to TQ2K's
http://www.xoutpost.com/x5-e53-forum/...highlight=tq2k