DD subs are one of the best... that is a really good choice...
but I think if you want sound quality and go with the factory logic system you do not need a powerful sub like driven with over 1000 watt rms... that sub will be too powerful with the factory system... you must upgrade the other speakers and should buy powerful, nice, and expensive
ones...
For me best is to use a sub with built in amplifier, they occupy very small space and can sound good... infinity has a sub like that like 200 watt rms and very small... I do not exactly remember the model...
For the design, I must say I did not like... you should need a small box for sound quality... my friend has a competetion box that seems like your box
(ported and big...)
anyway, dd subs are great! you will again and again modify the system after some time...