Can't help with the THX 887, but can give a +1 on the LS.
Before I got my LS, I was a bit concerned about Amir's review and the relatively 'poor' SINAD. Then it hit that the number was impacted by the weird 30Hz PS artifact, and the 'real audibility' SINAD was probably more like 105 - 110. I bought.
The LS has been the best of anything I've tried for my HE400i. Most solid, impactful bass. ES100, BTR3 didn't come close - and both got sent back. An NX3s I kept for portability, and while it comes close, its still a cut below.
Like you, I keep wondering 'what am I missing' by not 'upgrading' to - whatever. Then I saw the Qudelix for $110. It had what I was really missing - a 10 band PEQ. (I will Not put a PC in my chain. Ever). Got it, put it feeding the LS - result: a 'Happy Camper' (bye-bye HE400i shrill peak).
Perhaps you already have PEQ ability. But if not, you might just consider something to provide it (like the Qudelix) before spending to directly replace the LS..
Just one members experience and view.
Have Fun!