the only way to do it is to mount your drivers into a wall and have the rear waves going into an anechoic chamber. That should provide crystal clear sound. Thats the main problem with box loudspeakers theres not enough absorption of rear energy.
What in your mind represents real technological advancement.
To be a real advancement the technology must improve the sound quality. Just extending the bass or the high end can't be call an advancement if it doesn't sound better. If the bass goes " lower " but is muddy or the highs go higher but are " bright and forward and irritating " then that does not improve the listening experience. So the question is what improvements make a speaker more enjoyable to listen to.