The difference in cable length for HDMI that you are refrencing is typically to account for HDCP negotiation which doesn’t sound like the issue you are having. Does the issue occur with bitstreamed audio (e.g. sending Dolby Digital audio direct to AVR for decoding) as well as with PCM audio (this is audio that’s already been decoded by the PC)? Can you plug the HDMI cable direct to your display and still get the issue?
