Hi,
Welcome to BeoWorld
Congratulations with your Beosystem 5500 .
Regarding control by Beolink 5000,
unfortunately not in 2-way mode, only in 1-way mode.
The 2-way of the MCP (5500) is different from Beolink 5000/7000.
Having said that, i'm somewhat puzzled about my Beomaster 6500
being able to cope (2-way) with MCP 6500, as well as Beolink 5000 and Beolink 7000....
AUX on Beomaster : SHIFT + RADIO
(SHIFT + source-button gives acces to several other sources)
Regarding the Datalink-issue, i don't know,
but i'm pretty sure that fellow members can help you with that