I've bought my pi almost half a year ago but had no idea what to do with it until last week. To start off with, i must say that my desktop pc takes really long to boot. Last week i came back from the university and wanted to hear some music, but the thought of turning on my pc or to crawl under my desk to connect my phone with my audiosystem really turned me off. So my idea was to connect my desktop pc and my raspberry pi to my audio system and be able to connect my phone via bluetooth to my pi. i coudnt find anything about such a cable (reverse y-aux-cable without switch) so i build one myself for 5 bucks and it worked fine (the other option would buying a mixer for at least 60$) . Used a tutorial to set up bluetooth on startup and stream audio via BT. And this evening i set up everything and it works like a charm.

Just wanted to share my story :) , if somebody needs the circuit layout for the cable, i am glad to share it.

Sorry for my bad english, tried my best.

The tutorial for the bluetooth-audio-connection: http://www.instructables.com/id/Turn-your-Raspberry-Pi-into-a-Portable-Bluetooth-A/