I have beeen able to mostly eliminate the "booms" during HDMI switching and resolution switching be doing an HDMI reset.
Mostly, the problem occurs with a PS3. My HDTV is a Sony XBR4. Just cut power to everything (unplug from wall), unplug every HDMI cable, wait 15 minutes or so, then re-plug and power back up. Usually it fixes the problem. If I do any further swapping of HDMI cables, the problem usually comes back until I do another full reset.
Also, some ports on the T775/T785 seem to be less susceptible to it than others. My PS3 likes Port 1 on my T775 best.
This all sounds kind of silly and doesn't make much sense. I think it's all just a slight timing issue affected by impedance stackup in all the cables and connections. The "right" stackup allows the NAD to switch correctly and keep the sound muted until the switching is completed.
I also agree that even with these residual issues, the NAD is still an excellent choice. I went against my better judgement and bought a Sony receiver first figuring it would integrate better with the Sony HDTV and sources (I had a Sony standalone Blu-ray before the PS3), but it was a major disappointment. No other receiver has an Audyssey room correction implementation that sounds as good as NAD's, and the 100% assignable input configuration with full editing on source names is also superior to anything else I've seen.
HK's latest receivers have had a LOT of trouble. Onkyo and Integra sound harsh to me and run way too hot. Yamaha is OK but sounds a little less harsh, but still runs pretty hot. Sony is overpriced and ladened with useless features. Denon is about the best next to NAD, but still very "Japanese" with far too many extra features I won't use.
Perhaps when Arcam and other higher-mid-level companies get their HDMI receivers out there will be a better option than NAD, but for now I haven't seen it.