I don't think Axiom did anything to the tweeter in v3. The changes came in v4. I think only the cross-over changed in v3 to take advantage of new learnings from The Family of Curves. Then Ian laid the boots to Andrew and told him to put more Mojo in the tweeter. So Andrew did and brilliantly so.
Edit: the tweeter was changed in v3 but the changes didn't go far enough. I think a die cast aluminum face plate was added but all else stayed the same. There were some complaints about it and that's when Andrew got to work.
The new imaging and soundstage you hear in the v4 came about in the v3. Then some refinements were made in v4. The white aluminum dustcaps were v3 and so were the magnetic grilles. The M3s (and maybe M2s) got some "real" cross-overs with better parts.
v4 brought improved mid-woofers, tweeters, and standard woofers including the HP woofer. And as I said before, the cross-overs were improved. I think the improved cabinet bracing came with v4. The subs got improved including the amps, sphincters and bracing. The sealed subs got tightened up with improved DSP code and bracing.
And I strongly suspect somewhere along the way, the MDF changed. And as of maybe the last year, the weight has been reduced but the sound has not been affected. I've done head-to-head tests of the heavy v4 160 and M5 with the lighter versions and there is no difference.
Engineering got real, real serious between v3 and v4!
