Regarding Stax - I don't own, nor have I tried the realizer. But I have a couple of thoughts..
- Very low distortion - we are talking about 0.1-0.3% 20-20kHz for the basic 207
- FR without extreme peaks and dips that are hard to equalize, as seen with many dynamics
- Treble extending all the way to 20 kHz, which add to spacial cues. 'Stats oftenmost have very impressive high treble extension
- Last, and most importantly, the 'stats I have tried (especially the lambdas) sound like speakers next to your ears. Try comparing that to hd800, which by itself tries to emulate a proper soundstage by displacement of the driver. I guess one would (ideally) want 2 uncolored planar wave units right next to the ears with the realizer for optimum results.
Just some thoughts.