Yeah I knew there was a center, but I'm also looking for a good large circular sound stage headphone as opposed to a cramped circular soundstage or a wide oval sound stage (as you have described). It IS a lot to ask, I do realize that. Maybe it's just purely out of the $300-$400 price point.
From my point of view, this is not about money, It's about technology limitations.
The expensive state of the art is not that far from K70x in terms of soundstage, most knowledgeable people who have owned and enjoyed K701/2 and now own HD800 (the best headphone for soundstage out there) can confirm that there are some subtle differences, but that's all you'll hear for now, something a little bit better and just that.
Soundstage is also extremely recording dependant, and with headphones, going binaural is very important in order to go a step closer to real life. For sure there aren't many binaural recordings, and we haven't talked yet about the fact that there are some very good binaural recordings and some that are just ok.
For a soundstage lover, big bookshelf speakers or floorstanders in a treated room are the best way to go, much easier for our brains!
The perception of soundstage with headphones is really personal and complex.
You can drive your car using a very nice headphone and don't perceive a coherent soundstage, then you pick the same headphone and play the same album sitting comfortable in a silent room at home, close your eyes and after 2 songs you can tell exactly where everyone is on the recording.
I don't think we can say that a certanin headphone has a 3-blobs soundstage (or a 2-blobs soundstage), neither boxy soundstage, or any other variant. I'm sure that's a way to describe how some people, listening to some recordings, under certain conditions perceive soundstage, nothing more.