Is DEQX a game changer?

Al, yes, the minimum measurement distance will vary depending on speaker size, less for a two way and more for a large panel speaker. There are no hard and fast rules. Obviously the further away you put the mic the harder it is to get a reflection free measurement.

Software manual is here: http://www.deqx.com/downloads/DEQX-Cal_Installers_manual_v2.91.pdf

Just wanted to say that I have used the technique of building a "box" of acoustic panels around a speaker for in room measurements. I have a bunch of Realtraps HF (not the standard kind) I use for this, mostly because they have metal frames and so stay upright and don't mind being transported from place to place unlike regular resin hardened panels which are not fully wrapped on the back side with fabric.

It's important to realize that you do not have to use the speaker correction functionality (the part of the DSP that is best with measurements taken outside).

The DEQX has other functions - digital pre-amp, digital crossover and room correction that make it great even without the speaker correction.

The better the speakers the less improvement from speaker correction (as the drivers will be closer to flat and better pair matched).

With speakers like YG or ATC the improvements from speaker correction are small (but still noticeable).

The sound quality of the DEQX is good enough without speaker correction that I think it stands up as an exceptional product even without turning on the speaker correction.

The group delay plot should be relatively smooth post windowing, and should not have any "spikes", if you have those it is a sign of reflections corrupting the measurement.