I wish I could help, Raff, but I had to look up sibilance in the dictionary to find out what it was, so you can see that my level of audio sophistication may come up short. It seems like a problem you could only have with FM radio or the likes, and not with digital.
I guess you would have already tried all the usual suspects like switching cables and such. This may be one of those ones where certain boxes when hooked together with HDMI just don't like each other.
Possibly settings from the source or within the display related to digital connections? If the display is HDMI then typically you get analog inputs for it for DVI sources; there is a bypass anyway...
The display is HDMI and the H20 is HDMI, no DVI to use.
I have never tested it but I guess you have and it ignores the analog inputs if you use HDMI? HDMI did not always support digital audio did it? Could'a swore there was a brief period where it didn't... (inferring there should be a way to use analog inputs)