I own 7006 towers. I demoed all of the 700x towers before I purchased.
The Def Tech Supertowers, while freagin sweet, are not a substitute for a dedicated sub. They just don't get that low or have the tuned enclosure to provide deep tones.
That being said, $800 for that pair is SICK. If you can get them, go for it. That's less than a single would cost you new.