Too late for the OP, but I wanted to reply to the comment about mains hum.
I believe what Stereophile documented was the self-noise of the system, not mains hum. Mine don't hum, but you can hear hiss if you put your ear to the tweeter. You'll find similar comments about hiss from some modern active DSP systems (e.g. Dutch & Dutch).
My Xda (the amp/dsp box) did make an annoying mechanical whine (not transmitted to the speakers), probably from the switching power supply. I sent it in to NHT, and they were not able to fix the issue.
To me, this system is a lesson about undocumented, proprietary DSP systems. As far as I can determine, If my Xda stops functioning, there's no way to repurpose the digital crossover filters. Updating the amps and the DSP is also not an option without considerable hacking, or creating your own crossover filters from scratch.