I've had the 4306 for a couple of weeks now, I did not perform a direct comparison against the Pioneer. These two receivers were in the final running, I ended up going with the Denon because I liked the feature set, in particular the Ethernet connectivity, USB port, and I wanted to give Audyssey a shot. I figured if I wasn't happy I could always return the Denon for the Pioneer within 30 days of purchase. I paid about $1500 for the 4306 from an authorized dealer
I ended up being very pleased with the 4306, it replaced a Yam 2095 receiver I'd had for the past seven years. The setup for the 4306 is not trivial as it has settings for a variety of listening scenarios (Direct/Stereo/Multichannel/etc.).
For my room with my speakers, Audyssey worked very well, as a matter of fact it equalized the bass as well as the BFD I had been using with my Yam 2095. Additionally, if you're not happy with Audyssey, you still have the option of using the nine band/channel graphic equalizer, which I believe offers the same frequency type adjustments as the Pioneer MCACC system.
Below is an excerpt from a post I made about my experience with Audysssey, if you search this and other forums you will find users who love Audyssey, and those who are unhappy with it. I'm sure if you search you will also find users who prefer their MCACC turned off. Bottom line, I think you'll be happy with either receiver, be sure to buy from someone who will at least let you exchange for a different model if you're unhappy with your purchase.
I've had my 4306 for a week now, and have just compared the Audyssey EQ for the sub frequencies to the what I previously was getting with my Yam 2095 and a BFD. For my setup, there is no doubt that the 4306 w/ Audyssey is doing as good, if not better, as the Yam 2095 w/BFD. Here are the results:
4306 w/EQ on: 28Hz-140Hz, +/-4 dB
2095 w/BFD: 28Hz-140Hz, +/- 7dB
The two are actually fairly similar below 80Hz, the biggest difference between them is in the region between 80Hz-140Hz, where I assume the Audyssey is doing more than just sub correction, here are the results:
4306 w/EQ on: 80Hz-140Hz, +/-3 dB
2095 w/BFD: 80Hz-140Hz, +/- 6 dB
I'm using the crossovers recommended by Audyssey, which are:
60 Hz - Mains
80 Hz - Center
100 Hz - Surrounds
I've also checked all of the levels with Avia HT Setup Disk, and all of the channel levels are spot on.
One other interesting thing the Audyssey did, when I was looking at the response curves in the Graphic EQ, they were set for the most part +/- 2 dB of flat, with the exception of the 500Hz-1kHz region, here there was a -5dB cut for both the L & R speakers. I looked up the speaker's response curve (Norh 6.9 SM), and they have a 5dB peak starting at 500Hz and extending past 1kHz. So it looks like Audyssey is doing a good job of flattening out the sound field for a uniform response.
I realize not everyone has had similar experiences with Audyssey, but for me it is working about as good as could be expected. So far I like the results of having it engaged.