And yet again, to reiterate, in the spirit of "The Department of Redundancy Department".
From a practical standpoint:
(If you are starting from scratch) An AVR with Audyssey (or, maybe, the Yamaha and Pioneer equivalents) is by far the least expensive option to get a good implementation of an automated EQ system. You really are not paying extra for the additional channels of amplification and modern AVR's share the amp's capabilities such that, if you run them in stereo, the two channels have access to the resources that would normally go to the additional channels.
If you price AVR's against stereo receivers, you will see that you don't save much at all by going stereo (though there are other reasons you may prefer stereo), and from a feature standpoint, you cannot begin to compete with stereo gear. Such is the benefit of mass production - not that many buying stereo gear as opposed to having a TV in every room.
Since you already have an amp you are happy with, that makes the $ issue a little different.
Of course, if you have to buy a new AVR, that also equates to the expense of buying a miniDSP as Wayne mentions above.