I would like to know exactly what the SDEC box does ?
Actually you are very close to the source of that technology. Harman bought BSS audio a few years back:
http://bssaudio.com/en-US.
BSS makes extensive set of DSP hardware product. They are programmed using their software, London Architect in countless venues to shape sound reproduction.
What Harman did was use their audio research to implement room EQ and crossover using BSS hardware. They take standard BSS Audio DSP rack units, pre-program them with their software and sell them under the SDEC and JBL Synthesis brands.
Unlike all other competing systems, the room EQ from JBL does NOT come with ability to measure anything. Dealers are loaned an 8-microphone system that also uses BSS hardware to measure the room response. The software is told what loudspeakers you have and if it is one of Harman's it will know its capabilities so it will not try to ask them to unnatural things like boosting their bass frequencies and create a lot of distortions. For this reason, it is not very DIY friendly although post correction, you can mess with the system created filters.
There are some key benefits that come with this (please read all of this with a grain of salt given the commercial interest my company has with Harman and my personal relationship with them):
1. With 8-mic measurement system, you can repeat the process as many times you want and evolve your room EQ. With a single mic that you walk around there is no way to duplicate the results a second time.
2. The EQ software called ARCOS, is able and will program multiple subs differently. It can apply independent filter, delay and level to each one to get them to all blend as optimally as possible with each of your loudspeakers. See this article on this technology called SFM:
http://www.madronadigital.com/Library/Computer Optimization of Acoustics.html
3. Crossover optimizations between the sub and each loudspeaker. Again, while using multiple subs and multiple loudspeakers, the system will try to find the optimal filter settings so that each loudspeaker blends well with the subs.
4. Once these things are done, then overall set of loudspeakers -- mains and subs -- can be treated as one and global EQ applied to them just like other systems do. If one skips the previous steps, then the correction is not nearly as effective. See this article on this and overall UI for the system:
http://www.madronadigital.com/Library/BassOptimization.html
5. The system is highly tunable. I can turn any correction filter on and off independently. I can listen by ear and see if a lift of 3 db at 68 Hz really made things better or just made the graph pretty. You can literally close your eyes and click with a mouse on a checkbox for that filter to hear the effect. And of course can choose to turn off all filters above certain frequency.
Everything I described works with passive loudspeakers. Where M2 is different is that it also comes with "anechoic" correction filters and crossovers in the DSP/SDEC processor.
Back to the hardware, the version I have and what started it is a two-box system:
http://www.madronadigital.com/Showroom/HomeTheater.html
You get 14 output channels out of the system which you can configure to drive loudspeakers from 1 to 3 way and N number of them around the room. There are now other versions with different number of inputs and outputs.
I am not an expert on what you get when you buy the Crown amps with DSP in them. My sense is that it is a subset of all of this but I don't know. I can find out though.