I've owned my TX-NR-NR709 now for about a year, and I am having concerns about distorted sound when listening to music; specifically with sources coming into the receiver via HDMI. I've heard that these units have had problems with HDMI boards, overheating, etc. Sometimes when watching cable TV over HDMI, the picture and audio will freeze, but I'm not sure if this is a result of the receiver or the source; I'm guessing it's the cable box because I haven't encountered this issue with my XBox 360 or Blu-Ray.
What I'm experiencing is sort of an almost analogue tube sounding, overly warm compressed sound, when listening to music at moderate volumes and pushing the amp. It seems to get worse over time, the longer I am playing music at high volumes: frequencies start to sound 'bunched up', muddy, and compressed, and vocals especially sound off - shrill and artificial, almost like a bad MP3 sound. I don't frequently listen at ridiculously loud volume levels, but -25-20 dB is common, sometimes pushing up to the -15-10 dB for low level recordings with lots of dynamic range. The amp has adequate ventilation and I'm noticing that when placing my hand about the vents on top the amp, when it's running at high volumes, it really doesn't feel that warm at all.
This distorted sound all started with my old receiver which didn't support HDMI. I was using my Blu-Ray as my primary audio player, and had the Blu-Ray run into the TV via HDMI, with my other components, and was using a single optical digitial cable out to the Harman Kardon receiver I was using at the time. One day, I was messing with the settings on the Blu-Ray while listening to music (ie, switching between bitstream audiophile, and linear PCM, for output) and all of the sudden, this horrible, digital sounding mess was being blasted through my speakers at high volumes: it sounded like what might happen if you put a data CD like a PC game into a regular CD player and tried to play it back. In the past, I do recall reading disclaimers about putting data discs in CD players, and it's potential to damage equipment or speakers.
Following this, I noticed that the CD I put on next did have that muddy, overly shrill distorted sound to it. The issue seemed to remain ever since this incident, but doesn't seem to be apparent with sources that aren't consistently driving the amp and speakers at high levels (ie, when watching TV or movies). I'm wondering if the distortion I'm hearing could actually be a result of damage done to the speaker crossovers, or another component in the speaker, as a result of this digital noise being blasted through my speakers? Is there any objective way to test my speakers or amp, say, with a voltmeter, to determine if there is damage or distortion? Thanks to any and all who can offer any insight on this!