I've been looking for a good sub to round out my rig, and I've taken some interest in some of the subwoofer kits sold by Parts Express. They seem like a great economical way of getting a very good sub, and having fun building it (I'm big on DIY).

I'm interested in the 10", 240 watt Dayton T1003 kit:
www partsexpress com/pe/showdetl.cfm?&Partnumber=300-760

Or the 12", 500 watt Dayton T1203 kit:
www partsexpress com/pe/showdetl.cfm?&Partnumber=300-762

(Links de-linked because apparently I'm too new. Sorry for the inconvenience.)

Details about my setup:
- 50" 1080P Samsung DLP HDTV display
- Onkyo 704 receiver
- Boston Acoustics VR950 front tower speakers
- Boston Acoustics VR910 center channel
- Boston Acoustics satellites (can't remember the model number).

I live in an apartment building, but it's older and has quite thick, probably cannon-proof walls. But I'd rather not piss off my neighbors too much.

I primarily use my home theater for watching movies or listening to music. I'm more interested in tight, high quality bass than pure volume.

Opinions? Should I go in a completely different direction?

To be honest, they aren't really the best value at this price. You're better off either buying a finished sub or going all out with DIY and building something really special.

Many posts on the DIY boards say the Dayton Reference 12" driver, the RSS315HF, is better than the Titanic
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=295-464
I've also read quite a few posts saying this woofer is about as good as you can do for the money right now.
PE has just come out with a new 'project kit' featuring this woofer:
http://www.partsexpress.com/projectshowcase/rs1200/index.cfm.

Now, you could save building your own cabinet, and you might want to consider other amps such as the new Elemental Designs amps, but from what I read, you're not going to do much if any better on the woofer for the $ :)

ggunnell is correct. The RSS315HF is an exceptional driver for the $$$.