Before a new HDMI cable is purchased for the HDMI CEC compatibility, you should better times - if it exists - try an old HDMI cable. For me it worked without any problems anyway.
The films are played all completely smoothly and the CPU's burden of Raspberry here with about 10% utilization barely. The CPU temperature is about 50 degrees (room temperature 20 degrees), so quite low. Because I had but bought in advance heatsink, I will also install and see if they cause any appreciable drop in temperature. (UPDATE) With the two possible heat sinks the temperature dropped during the movie playback at about 43-45 degrees, though this probably should have no effect on the life values call the chips.
QNAP and Raspberry are connected via a 100 Mbit / s LAN cable, which is perfectly adequate for my video. Since the Raspberry leaves off by software namely, for switching must always briefly disconnected from the mains but, I'll get me a switch connector to the power supply does not always have to unplug. Although the Raspberry low power consumption, but does not always have still depend on network for me.
Addendum: As a well-functioning mouse to complete the remote control, I now use the Logitech M185.