Looking at a picture of the rear, one optical looks like it has a TV symbol, the other doesn't. My guess would be, one used for audio from TV, the other connected to a different source, most likely for music.
So, you could use the optical out from you Android box as you mention. Output music to the DALI via that rather than having to have the TV on to play music. If you've got an app on your phone or tablet for the software you use on the Android box, then you can use that rather than having the TV on to see what you are selecting.
I do a similar thing with a RPi3 and Kodi. I have a DAC board on the Pi and use RCA to my amp, so I can listen to music without having to have the TV on to pass on audio. I use an app to control Kodi, so I can select music without having to have the TV on to see what I'm selecting.