@dvdboulet
If you haven't yet, you might want to check out the Spatial forum over at audiocircle. Reports on the X5 and X3 are starting to trickle in there.
People who've heard both the new M and X series state the AMT driver offers more controlled directivity (like the old M3's point source nature), where the sapphire dome is more widespread and potentially offering a wider sweet spot. Surprising to me is that people specifically mention the great bass response in the M3 Sapphire where one review I read on the X3 mentioned subs could be a requirement for bass lovers.
The X5 was going to be my next speaker until I lucked into a great deal on the Tannoy Legacy Arden. I only mention the Arden since you're interested in bass. This speaker allowed me to take (2) 15" sealed subs out of my system. They offer an acoustic weight that I've not gotten out of any other speaker in my home.
Best of luck with the Spatial research, Clayton has some amazing engineering talent.