Not all TVs can handle surround sound on a HDMI input
With a home theatre PC connected to a TV via HDMI, Windows reveals that the TV only supports stereo sound even though the TV has a HDMI ARC connection to an AV receiver which is powered on; I also had an issue that the AV receiver does not always retain the input setting for routing the HTPC video through to the TV in standby.
So I connected a second HDMI cable to the HTPC and set it to duplicate the video outputs, but I had random audio dropouts when playing content with surround sound being passed to the AV receiver (dropouts did not occur when I replayed the content where it dropped out) but I did not have this issue when only one video output on the HTPC is used - this could be a processing problem.
Then I hacked a HDMI angle adapator which can be easily disassembled with a CMOS 4016 quad bidirectional analog switch to disconnect the Display Data Channel (DDC - 2 lines)/Consumer Electronics Control (CEC)/Hot Plug Detect (HPD) lines on the HDMI connection (to tell the HTPC that a display is disconnected) which fixed this problem.
So I connected a second HDMI cable to the HTPC and set it to duplicate the video outputs, but I had random audio dropouts when playing content with surround sound being passed to the AV receiver (dropouts did not occur when I replayed the content where it dropped out) but I did not have this issue when only one video output on the HTPC is used - this could be a processing problem.
Then I hacked a HDMI angle adapator which can be easily disassembled with a CMOS 4016 quad bidirectional analog switch to disconnect the Display Data Channel (DDC - 2 lines)/Consumer Electronics Control (CEC)/Hot Plug Detect (HPD) lines on the HDMI connection (to tell the HTPC that a display is disconnected) which fixed this problem.