I fundamentally agree with Pete here. I think, performance wise, there is no getting around the notion that really deep bass requires either a really big box or an obscenely powered amp; none of the powered main speakers I've seen satisfies those tenets to my satisfaction.
I'll offer a couple of other observations.
First, while having powered subs integrated into the speaker (main or center) seems like an elegant solution, it could be challenging to implement; each one of those powered subs needs not only a signal from your receiver, but also AC power from the wall. I don't know about you, but I already have enough trouble with my cords and number of outlets.
Second, integrating the subs robs you of placement flexibility that might be critical. It is extremely unlikely that the optimal placement of the main speaker(s) will also be the optimal placement for the subwoofer. Having spent a fair amount of time repositioning both my speakers and my sub, I can report that room boundaries and speaker placement made a profound difference to me. Being able to place the sub independent of the mains was pretty important in my room.
As for the Def Techs - many people love them. They are, by most accounts, a really well engineered line of speakers. Personally, I always hated the big-black-sock design.
Modern A/V receivers have pretty good bass management, and my opinion is that allowing a dedicated sub to handle the LFE provides the most flexibility and highest performance in both the short and long term.
Enjoy your journey. Let us know how everything works out.
