Let me preface this by saying, I'm a DefTech fan and owner, all of my bed layer of speakers have powered woofers/subs, so don't think I'm just automatically discounting them because of what I've read or heard on the net.
Here's the deal with speakers with powered subs built in, most of the original designs were to aid in low end to create a truly full range speaker (and this still stands today) the concept of using them as essentially a bookshelf on top of a sub was originally an after thought in the late 90's when home theatre started to become popular, and is to this day, more of selling point to those who either don't know that they really won't work properly as Subs or who, like in your case, just simply can't use separate Subs.
So, "can" you use them as a bookshelf/Sub combo....yes.
Will they play as low or have proper placement...no.
But, sometimes you just have to do, what you have to do, they're better than no sub at all and if later down the road you change rooms or can add a Sub, you'll have a good full range speaker on hand.
But....
Honestly you really have to go out and listen to them first. Since your in a position where you "have" to come up with a solution no matter what, your real issue here may actually be whether you even like DefTech's sound or not, esp. when it comes to bi-poles. People tend to have Love / Hate feelings about them, and mostly with H/T. So you need to listen to them to decide where "you" stand when it comes to their sound, then just make the best of your Sub situation from there.
