How Can I Display Firestick Content Using the Big Screen App In Metaquest 3

I wish to use my Metaquest 3 Headset as a monitor to display My Firestick content in the Big Screen App. I've being successful - so far - by connecting my Firestick to an HDMI Splitter box which is connected to my TV and a Capture Card which is then cabled to my Headset. I can view all my Firestick content in any of the VR Environments of my choosing. However, I've being unable to view my Firestick content whilst using the Big Screen App. I see YouTube, Prime, Pluto - all ready to go - on Big Screen - but not my Firestick. How do I add my Firestick to the Big Screen App? Does anyone know of a method I can use to solve this problem?