Your requirements are kind of tough. You basically want to fix any complaints people have about the Q701, while keeping the benefits. Honestly, I don't think you're going to find a headphone that will do all that, until you go to higher range.
My immediate thought was also for the SA5000 from sony. It's got an incredibly large soundstage, but it's a little bit dryer and not as smooth as the Q701. The HD600/HD650 will be smoother, but not nearly as open, unless you have a balance amplifier for them. The HE400 will be a little smoother, and very fast. I would recommend that headphone. Even though I own a HE-6, I was totally impressed by the HE-400 and its capabilities. Plus, you get a first pair of orthodynamic headphones. Incredible technology there.
Another option to consider is getting a proper headphone amplifier instead of getting a new pair of headphones. A dedicated amp will open the Q701 further and smooth it up a bit!