well. as I typed that last response, my xb90s came.
First thing I noticed. I can immediately tell high quality files from low ones.
couldn't do that with the fx40s. they all sounded the same even though I knew they were different.
also. soundstage.
these two factors alone are make the purchase worth it.
but you are right. subbass heaven.
and mids are SURPRISING.
At the moment though, the highs seem disconnected from the overall music presentation.
I am pleased with them (no sibilance and a tiny little eensy weensy sparkle).
But it seems like there's a gap between the mids and the highs.
might be the upper mids. I don't know.
I'll see what happens over the next day/week.
Perhaps a tip change will help too.
AND unfortunately. I look like an alien wearing these xb90s.
I have small ears.
BTW. XBA-4 $100.
http://www.ecrater.com/p/15970592/sony-xba-4sl-closed-quad?gps=1