NicklasT: It looks like I can just buy a new masterlink cable and hook it into my beosound 9000 but it only has one masterlink output I believe.
Welcome to BeoWorld!
That is correct... (1) ML on the 9000.
Buy the cable and you can test each of them separately.
If they all work and you decide to install them around the house... you'll obviously need more ML cable which can be bought in bulk (spool) and connectors from a dealer. You can simply create a daisychain. The question you will need to answer is how to connect it all together.
You can:
1.) Use a B&o 6 port ML hub
2.) Use B&o large and/or small junction boxes to accommodate splicing
3.) Rough splice them yourself
Search the site... lots of info on accomplishing this.