If the BS3200's ML port is not in use (or is only connected to audio devices, not TV/video) then you could simply use a Beolink Converter 1611 to provide an extra Aux input. Connect the BL1611 to the BS3200 by ML, and then connect the Spotify/streaming device to the BL1611's AAL socket.  With the BS3200 in A.OPT 2, the new source can be selected using any video source selection, TV, DVD etc. I'm sure you could also do this with a NL/ML converter, but am not experienced with this converter enough to described exactly how!