I kind of surprised you liked the Motion 15s considering the sound signature you mentioned upthread, I found the ML Motion series to be unpleasantly bright, but it could've been set up poorly in the BB when I demoed them, there's a ton of variation between different stores, and even between speakers in the same store with them. The first time I checked out the ML Electromotion ESLs I thought they sounded like junk, heard them at a different store and they sounded great.
The LS50 Wireless is supposed to be superior to the unpowered version, so it could have been a setup issue. Having built-in DSP and amps matched to the drivers should actually lead to a performance edge. I've only demoed the unpowered version and I thought they were nice enough, but I didn't think they sounded any better than my Elac Uni-Fis and weren't worth anywhere near twice the price. They are finished much more nicely though.
If you're going to add a sub (which again, I do recommend) make sure whichever pre-amp/amp or integrated you choose has built-in bass management and some form of room EQ. Aside from the Elac Element there's also the Paradigm PW Amp and the Martin Logan Forte (which is just a Paradigm PW Amp in a Martin Logan case) both of which offer great subwoofer integration and ARC room correction. They don't have the built-in USB DAC or a remote control like the Elac Element, however, you have to use a smartphone app to control them.