I checked my unit yesterday, it was also a hot day ambient wise, while streaming audio via Sonos for some 10hours the AVP was mildly warm, I also have a couple of fans drawing air across the AVP due to it being in a rack.
In the evening we watched a couple of movies, I also had the Air Conditioning running in the HT while watching the movies, didn't bother while streaming music. This is when I notice the temp does raise considerably especially the middle back top plate of the unit. I wouldn't deem it excessive although depends on how hot the boards are getting inside and if there are other boards on top of the video, which I'm guessing there will be. The video board would be running fairly hot when it is handling video for the change in temp, and must go into standby mode when audio only is being played.
"I may not always be RIGHT, but I'm never WRONG"