Distance to boundaries depends on the frequency range of interest. For example, if you're concerned with the interaction between components at a crosover above 300Hz, then a few feet distance from boundaries is plenty. You can gate the microphone input so that reflections are ignored.

About the subwoofer, I assume you're talking about the flux-stabilized B12. Eminence has already built a first prototype and found that the shorting ring reduced 2nd harmonics by more than 10dB, so that part was a success. But to get the reduction of harmonics down to the lowest frequencies requires a larger flux stabilization ring, so they are working on another type of magnetic structure. They'll build a second prototype using a structure that allows a larger ring, and they've told me that we're looking at around the end of the summer for a timeframe on that.