DSX does not prohibit rear surrounds - at least the processing mode does not. If you read the AV7005 manual (or, perhaps more easily, the Outlaw guide), though, it explains the processor's behavior when DSX or PLIIz is engaged. Here's the recap as I remember it:

Step 1: Configure as many speakers as you want. You can have 11.x channels set up in the processor's menus if you have the speakers connected.

Step 2: Choose the processing modes that you want to use. You can use Pro Logic IIx, DTS Neo:6, Dolby EX, Pro Logic IIz IIz (if height channels are enabled), DSX Height (if height channels are enabled), or DSX Wide (if wide channels are enabled). I don't think the AV7005 allows a DSX Height+Wide mode. What happens when using IIz or either DSX mode, though, is the back surrounds cease to be used.

It's all about the fine print, and the AV7005 is not the only PLIIz or DSX equipped product out there that includes such fine print in one way or another. Is it right that they appear to be hiding this stuff in the fine print? Not really. From that standpoint, it's nice that the Outlaw guide is more straightforward about how it actually works. I've seen so many instances of important (at least to me) details like this being buried in poorly-written documentation that I'm probably a little numb to it. Starting five years ago or so, we had "HDMI" receivers and processors that only supported HDMI for video switching, but you had to read the manual and look for the lack of instructions on how to configure HDMI as an audio input to know it. (That's why a good number of us were pleased with Outlaw for using DVI on the 990 and 1070/970 - same capabilities, and no doubt about how it worked.) This is just one more example of companies being vague (either intentionally or out of sloppiness or sheer laziness, I don't know which) about a feature's limitations.