I'm sorry to see that nobody has chimed in on your question. There is a WO section of the forum a little further down, but honestly, there just hasn't been a lot of interest in the forums in the DIY stuff lately. In the early days, the cost effective gear and DIY projects are what made this site. It seems to have grown more into the amplifier building.

Anywho, it's been a long, long time since I've build a WO - I loved it to death. Eventually I sold it when I decided to upgrade to a 21" (seriously!) home theater specific sub in a 17cu ft sealed box. That's what it took to interest me in changing. I don't recall what my original speakers were, but I eventually upgraded to some JBL W7 10" drivers because I really wanted to push air. Pretty much any decent car audio sub will sound good in the WO - but there were specific perimeters that Steve suggested we look for back in the day...I don't recall what they were, so you might have to do some digging in the WO section of the forum.