The 9.2 is for Audyessy's "full fat" DSX setup adding 4 more front speakers, 2 Height, 2 Width. but as I understand does not run the 2 surrond back chennels (otherwise this would be 11.2).
Apparantly they carried out a study in which they concluded, that due to the way we hear sound and the fact that our ears point forward, this is where the best use of additional channels would be heard and the surrond back benefits are minimal.
I have a standard 7.1 setup at the moment, with a new denon AVR1910, which does not have the DSX, but does have the Dolby version, PL IIzH.
I tried disconnecting my surround backs yesterday, after reading an artical on the AVR4310, and using the 2 height speakers instead.
This is only my personal opinion of course, but this made a lot of difference in 5.1 sound tracks, be it the lossy or the HD versions. The sound up front was so much more 3 dimensional and detailed.
I really did not notice the back surrond channels where missing, funny as it took me a while to get my wife's permission to intall them.
I will be over the next few days, removing my (in ceilings) surrond back channels and purchasing 2 front L/R speakers so my current front (in ceiling s) can be be used as the front height.
I surpose it comes down too, trying it for your self to see if you think it is of benefit, whether you can fit them in and in my case whether your partner has got to the point where she can't be bothered protesting to more speakers turning up in her lounge.