It was clever to realize you’re missing something other than SPL in your listening space.
Those LS50 drivers only offer so much Surface Area and that’s where I bet your upper bass / mids seem to be want for improvement.
Calculating driver SA on those upper bass / mids on any model you consider might be important. If driver SA (for frequencies of concern) is similar between LS50 vs. KEF “x” you might hedge your expectations for meaningful improvement. Keep in mind you wouldn’t care about total driver SA, as in larger cabinets much of the driver SA is crossed for sub duty.
Too bad you can’t buy a KEF line array.
But that would require DSP for optimal stereo, and you already mentioned that’s your boogabear, sssooo… 😆