I hope this information can help to find out the causes of the issues in the XXX4 line.
My SR 5004 has been working very well for two months.
Configuration: 2.0 (two Wharfedale Diamond 9.1, in bi-amp). The SR5004 is located on an open shelf, so that its top and right sides have free space for heat dissipation.
It is connected to an Oppo 980, via HDMI (coax for HDCD), so that only the following modes have been used so far: stereo (with Audyssey), source direct, pure direct and Dolby VS (for movies). I also listen to DVD-Audio and SACD (DSD mode), without any flaw. A Philips set-top box is also connected via HDMI.
My only complaint is that, even when setting HDMI video output resolution in the SR5004 to “Through”, there is a slight loss of colour and brightness, when compared to a direct connection between the Oppo 980 and the TV. I am using, between the receiver and the TV, a Belkin pure AV HDMI cable, 6 ft, certified for 1080p, 1.3. Oppo 980 is set to 720p resolution. Marantz suggested that I replace this cable with a 1440p one, which I think it is an expensive solution, since I use the equipment 90% for audio.