Airport Express - WiFi network extension with wireless speakers Background: I am considering an Airport Express (AE) to my room, but I am getting confusing information about how it can operate in different circumstances. I already have a router, with WiFi and LAN ports.
The AE would be connected by cable to currently owned router and I would also like to connect my Mac by wire to the AE.

Question: What I want to do is extend WiFi signal in our flat and also have the possibility to use my speakers wirelessly. Is it possible with the current AE?
Yes you can use the Airport Express to extend the wifi signal from your other router:
You just have to change the settings for your device in the Aiport utility to extend a network instead of creating a new one.

http://support.apple.com/kb/HT4145#

Yes you can use your speakers wirelessly. You just need to connect them to Airport Express. Apples technique is called Airplay:
https://www.apple.com/airportexpress/