What you attribute to REL subs can be found with other subs of very high quality. I agree it isnt as much the bass as how it opens the system up. 90% of subs are crossed over at too high a frequency. I still maintain it isnt his amps.
I have heard the AGDs at several shows and my take was a bit different. These were the best class D I have heard but they also, like other class D, had a 2 dimensional quality. The music didnt fully come off the front of the speakers. To really judge them I would need to listen to them in my room so perhaps this comment isnt entirely fair. My take away from one show was not how good the AGDs sounded, but how accomplished the pro speakers used were.