When having to meet certain space contraints, the DIY route is usually best. That is of course if you are up to the task. With a 9" height limitation you would want to look at a woofer with a somewhat low profile. The actual enclosure height will probably be around 7-1/2" allowing 1-1/2" for the woofer and feet (for enclosure). You are going to need a woofer with a mounting depth of no more than 6".
The Dayton Titanic MKIII 10" comes to mind as a good choice. $149.00
A pair of these sealed with 800-1000 watts and the Behinger eq/crossover unit would be a sweet set up.
The Dayton Quattro 12" can also fit the bill. $75.50
What are the other dimensions must the unit have to fit accordingly?