Roamio digital output and IHeartRadio

Greetings,
I have a standard Roamio with a fairly simple setup of HDMI to my oldish Sharp Aquos TV. I occasionally (when I'm alone) like to crank up the surround sound via the digital audio out of the Roamio to the digital audio optical input of my oldish Kenwood 1080VR surround receiver. The audio out works fine if I am watching OTA TV or Netflix. I can rattle my neighbors windows. If I decide to listen to the IHeartRadio app however, the digital audio out doesn't function. I have to listen though the TV speakers. Changing the Roamios audio setting from Dolby to PCM only accomplishes making the digital audio stop altogether. Just to be clear, everything always works through the TV's speakers. I have not tried signing up for a different music app to see if they have the same issue. I am wondering if perhaps IHeartRadio is not transmitted in Dolby and that is why it has no digital audio out or if that is even a reasonable train of thought. Any thoughts?

BTW-I do also have IHeartRadio on my Android and I can plug it into the aux (analog) input on the front my Kenwood and listen that way. It would just be less trouble to have it on the Roamio.☺

Thanks for your thoughts!