skelser, sounds like a HDMI firmware handshake issue between the receiver and the TV. My cable box will sometimes develop digital, echoed sound and I have to switch channels and go back to get the sound back to normal. Because TV providers, set top box manufacturers, receiver manufacturers, BluRay player manufacturer's, game console manufacturer's, etc. all use different HDMI standards, incompatibilities can happen at any time for any device or TV.
Since there are such a vast array of different devices and no standards in HDMI firmware Samsung cannot guarantee compatibility for everything on HDMI. All you can really do is make sure the software is up to date on the TV and the device in question. If it's a particular app that's having handshake problems specifically you could try talking to Denon support to see if its something that can be corrected in a patch. If the two are simply not compatible with each other then he may just need to use the Pandora App on the F8000's Smart Hub instead.
I'm no receiver expert but I troubleshoot TVs for an extended warranty company and that is my understanding of how the hardware and software interact in this situation. I'm leaving my job in a month or so for school but I've been troubleshooting TVs for over a year now and firmware incompatibilities cannot be resolved through hardware replacement because they are software induced problems.