Tim- I know you have never cared for the Def Tech speakers and since speakers are basically a matter of taste/preference, that's very understandable. And given the physics of your current setup, the KEF LS50s would work for you while the Def Techs would certainly not work. And even if they did, again, you don't like them so it's really a moot point. Listening to them in a Audio/Video showroom played through HT receivers or possibly some modest separates is not the same as hearing them and living with them long-term with the electronics I have been using with them. I believe I have owned these speakers now for around 6 years which is longer than lots of marriages last.
I was/am ready to try something new and after reading so many glowing reviews and understanding how much engineering went into the little LS50 jewels, I wanted to give them a try and see if they were *better* than my Def Techs and if could live with them long term. At first blush I thought I could. First impressions also led me to believing/wondering if the missing information from the LS50s I was hearing (or not hearing to be more technically correct) was all cabinet generated. Because the LS50s will make certain frequencies stand out more due to the thinness of only having a single very small coaxial driver in each cabinet loading into a fairly large room, they tended to make the soundstage appear to be wider and deeper. More time spent with the LS50s and reinstalling the Def Techs showed me this wasn't really true.
Given the size of my room and the levels I prefer to listen at, I zeroed in on the point where the LS50s shouldn't be pushed past. It was easy to find it with rock and roll, not quite as easy with jazz, but the point of no return is still there and you will find it unless you listen in a very small room at lower levels. In 6 or so years of listening to the Def Techs, I haven't come close to finding out where these speakers cry "uncle." It's someplace past the loudest listening level that I would ever tolerate.
So, are the LS50s damn good sounding speakers? Yes, they are. Would they be really good in a small room with a pair of subs? Why yes, they would. Am I willing to replace my Def Techs with the LS50s? Why no, I'm not. I don't regret buying the LS50s and it was a fun experience.