My DIY sub project, i have a link here, and a link within this one to the forum in Australia, which has a few construction pics, and heaps of ideas that have been changed a few times, basically it is a duel front firing, 12 inch peerlees 830952 drivers in a sealed enclosure, amp is still to be decided, waiting on a few replies from some one here with some amp experience..
http://www.avsforum.com/avs-vb/showthread.php?t=907932
Other reasons JBL are not so popular here is the price, a pair of L890 will set me back about $2500 australian ($2000 US) not sure how that compares to in the US..
My L820 were $880 AUs for the pair, at these price points there is a huge selection available, A lot of people here in that price point opt for Krix speakers which are a local product, so you get a lot of speaker for your coin.
They are much nicer to look at, have a great forward sound ( can be a tad bright ) They use peerless and vifa drivers in most applications, and veneers!