This is something I am still working on. There are ways to start entertainment using Android intents (more info) but that does not work with Sync at this time. It will be fixed in a future update when this bug is fixed: Starting Sync from Tasker does not work - #3 by Thomas
How are you planning to send that intent when pressing a button on the remote? Maybe we can build that into Hue Essentials.
See also the following: Automatically start/stop Sync on Android TV