I haven't heard these specific models of Def Techs and Viennas, BUT I have heard, side by side, both of their upscale monitors and floorstanders. To my ears it was like comparing a Hyundai to a Porsche. The Def Techs sounded harsh, flat, and cheap in comparison to the Viennas. And the pricing reflects the quality, unfortunately...because I really wanted those Viennas. I am now saving for some Baby Grand Beethovens.
But I repeat....I have no experience with the models you are considering. I suggest you let your ears (and your wallet) make the decision