... sound batting and/or weighting speakers ...

It's a 13 pound speaker including drivers! That's what is causing it! There is no recourse for a design like that being driven at higher levels!

so is the ls50. So are many bookshelf speakers. The blackthornes are $10k and weigh 12 pounds. 

To the OP; I mean no disdain in my comments. Here's the deal; I spent a LOT of time in earlier years working with inexpensive gear, desperate to make it sound all that. Sure, little improvements (which always seem to be big improvements without the experience of decades of system building) can be significant, but the gear is self-limiting; it will never be better than its inherent design. 

Physical, operational limitations on designs cannot be escaped through tweaking, weights, etc. To get much better, save up, work toward much better. You are currently with this speaker on the low end of performance in HiFi. That is NOT a dismissive comment, just an analysis of performance. I was there, in that zone for several years. The spectrum of performance is HUGE. There are many, many big performance leaps to attain, and in reality the ladder of improvement is endless. 

So, reach far higher! Make a change! Go for not just a fix, but a far superior  sound.  :)

To whom it may concern; I mean no disdain in my comments. Here's the deal; I spend a LOT of time around here watching people recommend spending money on upgrades. As if money grows on trees. Sure, big improvements can be had.... if you have big money to spend AND the time and inclination and ability to shop and compare. Even then however economic profit considerations will always limit design leaving lots of areas of improvement. These can be found all over the place, from speaker gaskets that seal but don't control vibrations to diodes and caps that are cheap and hold back performance. Because of all this the spectrum of performance manufacturers leave on the table is HUGE! There are many, many significant performance improvements that can be attained at little cost. The legs of the ladder are endless. 

So, keep reaching! Make a change! Go for not just one tweak, but many, for a far superior sound. :)

Physical, operational limitations on designs cannot be escaped through tweaking, weights, etc.

 A box is a box whether it costs 100 bucks or 10000 bucks. 

with all due respect, that is a completely ignorant statement from one of the self proclaimed greatest speaker designers / builders of all time, who’s actually never done either 😀