Finished up my ELX upgrade for the towers. The first tower was a fairly "dreadful" experience. I was a lucky winner of a cabinet that had narrow cutouts. My tolerances also seemed to diminish further inward towards the mounting corners due to variations in the finish. I initially measured 156.2mm with the original drivers installed on the outer edges, but further inward it resulted in 155.9mm.
Some loss of finish near the drivers and the cutouts and it eventually fit....4 hours of "fun" total doing that....sort of made me wonder if just sticking with the original V2 plan would've saved me the frustration. I eventually found a combo of selecting slightly smaller drivers in my kit plus finish removal (sanding) to the drivers and cutouts to finally get it completed.
The second tower had plenty of room to spare and was an easy and straight forward drop in replacement. No major issues with the 2nd tower at all. A polar opposite of the first tower.
I've listened to the towers and they sound great. I don't think I can add more description to what has already been said and will need time to evaluate further. It sort of feels like moving from a 2D to a 3D listening experience where on the v1 it was "flatter" and the ELX has more depth to the soundstage. With my room being 17'x14'x8', they are significant overkill for a room this size. I still have my Horizon upgrade kit in the box and am deciding if it is really necessary to complete the upgrade as I mostly listen to stereo and only use surround for gaming and the occasional movie. The "vanilla" v1 Horizon does well enough being about 9ft away and performing center dialog duty.