The folks at Sound in Motion have done a number of X5s and building a sub-box for the X is now a faster process. However history has shown that it's probably not worth to pre-build a number of boxes as for some magic reason demand will sudenly vanish
...
You may want to call Jim or Derek at Sound in Motion (
http://www.sound-in-motion.com ) and ask them how much they'd charge for building a custom box.
For those who plan to join us at Bimmerfest East 2005 you will be able to get a first hand look at the finish and fit of the subwoofer enclosure in my X.
- Jan