Of course it works like that. You go (digitally) into the KH750 and it also has the filters for the satelite speakers. KH120ii + KH750 would be a fullrange solution down to 20Hz.If the dsp allows almost ALL the bass to play through the kh750 and the rest of the spectrum on the kh120ii, it should theoretically better than just the kh150- acting as a three way.
but I doubt that it is optimised for this (allowing higher spl without distortion).
maybe the midwoofer on the kh120ii doesn’t go loud enough as the limiting factor here.