I have added a roku 2xd to my denon 4308ci via a monster hdmi. I get picture and sound when the roku is set to "stereo" and any roku HD DDplus program iI get picture and two-channel sound.
When I change the roku to "surround" and change say a Netflix hd and DD+ program (I.e. house of cards) to DD+, I lose the signal. This also happens on VUDU and HBO go when trying to watch any program encoded with Dolby Digital.
My Denon amp plays DD, DD true, Dts, etc. perfectly with blu ray and DD with Verizon set top box.
I even had an installer from our local (excellent) sound and video retailer and he could not figure it out. We called roku and denon support and they were no help.