Good s12" sub and subamp opinions needed

[Fustern]

Hey everyone,

I am new here and would like some of your expertise. I am looking to update an old home built passive sub wth a better subwoofer driver and use it in conjunction with a Velodyne VRP-1200 sub I have for a little deeper bottom end in my HT setup. The homebuilt sub I have is passive, but I would like to get a standalone sub amp (NOT plate amp) that I could use with it. I use my system for 70% HT and 30% music (rock, techno, new age, classical, etc, etc).

The home built sub's INTERIOR dimensions are : 24" x 16" x 9" (2 cubic feet)and it has a single port that is 3" wide and 4.5" long. It has an old Pioneer 12" sub in there now that I want to replace with something better.

I'd like to keep the combined subdriver and sub amp to $350 max.

Would love to hear your recommendations on a quality 12" sub that would go deeper than my Velodyne 29Hz (not considering home effect) and be able to have the phase continuously adjusted for optimum timing with respect to my Velodyne's output.

My system includes the following:

Denon AVR 787 A/V receiver 85watts x7 with sub output
Klipsch center, tower mains, surrounds
Pioneer surround back (book shelf)
Vizio 42" LCD
Samsung upconvert DVD

Links, model #'s, etc most appreciated!!