Confusion here - we are talking about Beomaster 5500, which doesn't
have a separate AUX input. It is in the same socket with TP2.
Anyway, it can be selected with A.TAPE2 on Beo4, which is exactly the same command as SHIFT-A.TAPE on Beolink 1000.
A.AUX sends a different code, but probably works too (my BM5500 is far away so I can't check).
Video
source commands should work as well, but the Beomaster needs to be
programmed to option 2, or it does absolutely nothing when receiving
them.