One key thing to keep in mind for RoomEQ systems like Dirac and Audyssey (and some but not all others) - is that they do more than just EQ.... we generically tend to refer to them as Room / Speaker EQ but perhaps the most important thing they do is impulse / phase response correction.
In terms of pure Speaker EQ, there are some complexities to incorporating an external EQ ( you need appropriate line levels out of the AV processor, and then power amps for the speakers ... so lots more components and cables than with a "simple" AVR)... but it is absolutely possible.
On the other hand - many of the better AVR/AVP based EQ setups, also allow for manual EQ should the user want to take that path - you sacrifice any sort of impulse/phase response adjustment that Dirac/Audyssey do, but you do have full manual EQ control.
Also with Dirac or with Audyssey (on current generation Denon) - you have the ability to tailor the target curve to your hearts content - ie: you can work within the room eq system, to do manual adjustments.
Given the capabilities and the pricing, in many/most cases, a manual and separate EQ box is simply not justifiable.... you can do the same job for less money in an AVP or AVR....
The processing capabilities and value, is why many stereo fans, have opted to go for an AVR - even if using external amps with the AVR.
There is a lot of tech for the money in most mid market high value AVR's.
