I'm not really sure what it is to be perfectly honest.  Everything sounds slightly higher pitched than it should and nasally.  One of those SA Sonys had a similar problem.

I get that.  It's a tonality that needs to be mitigated at 6khz.  It actually works more w/ pop and electronic genres so if you don't listen to genres like that then forget about it.  It's slighlty reminiscent of that totally fake Ultrasone tonality but nothing that ridiculous and absurd.  I actually found some Stax to be recessed in the upper mids making females vocals sound like they've been roiding it up tbh.


I wonder if you'll like them better from your Accuphase and a proficient non Craig amp.  PWD mk2 and Craig sound might be too much sugar on your cereal.


Edit - Well, like I've said, they aren't perfect and I'm still working on it.  They just have the best performance/price/genre bandwidth available I know of so far for me.  The fuzziness in the imaging is a combo of the mod ring width and BA/Tube selection.  The Super 7 images more precisely.  Could be 3 watts versus 1 watt or the C-core and tube selection.  Purrin wants to warm up the HD800 as much as possible.

I had both the normal and pro bias and ended up selling the Pro since I liked the normal a little more.  I've heard the Sigma404 briefly before and it was great as well.  You very well may end up liking the normal bias Sigma just the way it is though.  The extension in both directions isn't the best and they're not super detailed like other Stax, but the midrange is bomb.  Also, they like to be played within a certain volume range.  If you listen at loud levels they can get pretty boomy.  If you already have a 303 or 404 then by all means do the swap as you'd end up getting two superior headphones: a Sigma404 and a SR Lambda.

Pro/HE90? 

Hmm, I'm not seeing it.  Do you have a link?