I did a full evaluation of Pioneer 919 vs Denon 590 driving my Energy RC mini + S10.3 sub speaker system.
(1) First of all, about the heat of pioneer 919: I noticed a lot of people worry about the heat of pioneer. I am a thermal engineer, so I compare the Denon and the Pioneer design. I found in Denon box, the heatsink is much far away from the top cover vent, so the top cover does not heat up too much. In the Pioneer box, the heatsink is right under the top cover vent (very close), so the top cover is been direct heat up, making you feel very hot when you touch. I bet the heatsink temperature will be quite similar for Denon and Pioneer. So don't worry about the heat for pioneer. To some extend, Pioneer might be a even better design because the top cover acts like another heatsink to carry more heat out of the box, while for Denon, more heat are trapped inside the box.
(2) About Audyssey vs MCACC: I was amazed how close the results of these two system calibrated my speakers to my room acoustics. The channel level/distance, as well as the EQ settings by Audyssey and MCACC are almost the same. My room is not symmetric(with one side open to kitchen). There is big difference of bass level in different listening locations. Both Audyssey and MCACC did equally well in adjusting the bass response to make it sound much better. Audyssey MultiEQ can EQ sub channel, while MCACC's standing wave control and reverb control seems achieve similar result. Audyssey can do 6 point measurement, MCACC also has a 3 point measurement option (with reverb delay time adjustable) in prof eq setup. I would say Audyssey and MCACC perform quite close.
(3) I also pay much attention to the Denon's Dynamic EQ performance, as most of my listening are in mid low volume. Yes, Dynamic EQ did have significant effect, making my RC-mini sound much full in low volume. Somebody may even say it is too much. I found setting the reference offset at 5db or 10db help damping the Dynamic EQ effect. Now, go to the Pioneer 919, thanks to its capability of manual adjusting all the setting after MCACC setup, I can achieve similar effect of the Denon's Dynamic EQ. I saved the new setting to another memory set (you can save 6 different MCACC setings), When in use, I can handily switch between the settings, just like I also have the Dynamic EQ function. So the two receivers are still equally well in this regard.
(4) If there is any difference between the two, my feeling is that the pioneer's high frequency performance is better, give you more lively feeling, while the Denon's low end is slightly better, it may give you a fuller sound feeling. But all these can be adjusted by eq to your taste with either receiver. So you can achieve the same end result with both receivers.
(5) This is why in the end I choose Pioneer over Denon because pioneer offer the capability of full manual adjustable setting. (Denon can only adjust speaker setting, not EQ setting, if you want to keep Audyssey and Dynamic EQ on) My point is, there are two equally important things when it comes to good sound: First is to overcome the room acoustic problems, and the second is to adjust the sound to your preference because each person's taste is different. The MCACC and Audyssey's main job is the first one: overcoming the room acoustic problem. The receiver still need to offer the users the ability to adjust to their own taste. Otherwise you are only half way to your own dreaming good sound.
(6)RC-mini setup: Before the Energy RC-mini, I owned some PSB, Boston, Polk, and Athena speakers. The first impression when I heard the RC mini, I immediately noticed two improvements: better and more detail mid-range,as well as better soundstage and image. the sweet spot is also wider. I remembered I was a bit surprise when I read review of RC mini from GoodSound saying the midrange voice is a bit forward, standing out for RCmini, because all other reviews said RC line is quite neutural at all frequency. But when I heard it by myself, I also noticed the same. Both Audyssey and MCACC auto setup also showed this and set eq at 1-2khz about -3db to -4db lower than other bands. For cross-over setting, I found 120Hz(Denon) or 150Hz (pioneer) is better than 100Hz for RC mini. I also found setting main speaker to 'large' and using 'plus' (sub+main) for subwoofer seting generated the best transition from the RC-mini to the S10.3 sub. With this setting, the midbass and upperbass are much full for RC-mini, and there is no double bass issue because rc-mini drop quickly as frequency goes lower. After these setting and either Audyssey or MCACC calibration, the RC mini+S10.3 sounds unbelievable.