With my cheap tweaks the KEF Q100 sounds much better than original, much better.
Bit brighter -> With a good soft equalizer you can soften the trebble (with Q=0.7 is the best). Or more easy, turn the speakers a little to the walls.
KEF LS50 needs more separation from all the walls, not just from the back. 79 Hz at -3dB -> you need a subwoofer.
KEF LS50 has true 83 dB and the minimum impedance is almost 3 Ohms -> it needs more power to sound OK.
Both sound better on supports.
KEF LS50: 7.2Kg (15.8lbs)
KEF Q100: 5.9Kg (13.0lbs). You can add mass to the case.