I have to say, I'm really really really liking the XBA-40. The tweaks have been subtle but meaningful. The XBA-4 was deeply flawed (and as much I liked the XBA-4 I don't think anyone can argue that metallic tinge wasn't just plain odd). The XBA-40 largely corrects that (on a low impedance source anyway) and brings with it a deliciously rounded low-end.
It's still sounds muffled and congested. In fact it probably sounds even moreso now, once the metallic ring is gone. It's by no means balanced, and it quite even possibly qualifies as a basshead IEM.
But I don't think I have ever heard a better earphone for electronica or synthpop. It's visceral and holographic and ethereal. It's detailed but completely non-fatiguing. I think I like it as much if not more than my (now long gone) SM3's.
And at $200 from Amazon.co.jp / Tenso I think it's a steal provided this is the sound you want.
Sounds compelling, I will have to try one out next time I drop by the city. the metallic tone was the only thing that bothered me with the xba4.