Amirm, Great article, I wish I had thought to find it earlier! I have been experiencing poor HDMI sound for ages. Initially I just had a good old Sansui stereo amp with a pair of Tannoys, fed from the headphone output on a small ASUS laptop which gets its content over a Gigabit LAN. This analogue sound was really very good, but my wifey didn't like the look of the old black Sansui nor the Tannoys (too big and wrong colour), and of course it was just stereo, no surround.
I changed to a JBL sound bar + subwoofer combo, the 'phasey' and distorted sound from which just drove me crazy, and in any case it was unreliable and a total waste of money. When it failed the second time (power supply first, then the Bluetooth to the Subbie) I replaced it with an Onkyo 7.1 setup which I'm horrified to say is exhibiting the same annoying sound. The "grit" I'm hearing is a bit like amplifier crossover distortion - but not limited to quiet signals - mixed with broadband intermodulation distortion, and all this fuzz is affected by the nature of the content. Some barely has it, some is almost unlistenable.
It seems the culprit is the ASUS laptop which accesses our videos over the LAN, just using VLC or PotPlayer. The HDMI picture is great, no complaints, but the HDMI audio is very disappointing. If I access the LAN content through our Sony BD player the audio is markedly better, but not as good as it is straight off a BD.
I'm wondering if you have thought of measuring tones from say, an MKV or an MP4 video with perhaps some colour bars or unrelated video through such a Home Theatre PC system which must be pretty common these days. I hadn't given it much thought, but now I realise that my ASUS laptop being used as a HTPC has to convert the audio and video from the mp4 / mkv files on the NAS to HDMI and that like anything else electronic there must be different quality chipsets for that purpose. I think there is a huge potential for very inferior HDMI sound in this common sort of setup whether the source material is originating from a NAS, a local HDD or a USB thumbdrive just plugged into the HTPC. It would be fantastic to get some idea of what HDMI chipsets are high quality and what manufacturers are making Laptops / mini PCs / etc. that can produce the high quality HDMI audio we are seeking.