Ahh, that makes things much easier

How about a Rainbow Amboss? A few people have the Vanadiums, but i'm yet to see a car with a Hammer or Amboss.
The Amboss is rated at 550w rms, and if they are like anything else Rainbow they sholud be built like a tank and sound fantastic.
Oz Matrix a few people have, but they are still fairly rare. Definately one I would consider !!
The high end DLS subs (UR12 I think) are said to be bloody good, and have around 500w power handling I think. There wouldn't be too many people around with those.
The Focal 33KX and Rainbow Vanadium are two of the nicest Sq subs around seemingly. However both are heavilly biased towards SQ at the sacrifice of SPL potential. that's not to say they are gutless (I know for a fact the Rainbow has some guts) but they wont likely hit any huge DB numbers if you ever want to impress your mates..
Any reason for not wanting DD? If good sq and loud is what you want, they may be just what you are after.
Alpine Type X again, is another option. I've heard good things about these, but if you want something 'different' then they are probably the last thing you'd want.
Vibe could be an option, but they dont realy have anythig in that price range i dont think, The Blackair is cheaper, and the Space is around $800 or thereabouts.
Umm who else....
Boston G5, Crossfire XT, JL Audio W6 (if you can find a second hand one),
Treo and Soundstream may have some good options as well?
The TDX I have heard running off some high quality gear and it didn't really impress me that much. wouldn't consider it on par with the Vanadium or IDMAX if that listening experience was anything to go by. Also graphed up pretty poorly whe I modelled them in BBP, however I don't like to base opinions purely on graphs and estimates, so I would like to hear another just to confirm before attacking their reputation for good.