I'm bit late. But you can't transfer music trough your bluetooth in Volvo. Mainly it is because the quality of the normal bluetooth is horrible and only in mono. The quality of the music would be so bad that no one would actually use it.
Also on a note, you don't have the AUX-plug because you don't have premium-sound package in your Volvo. Only way to get the AUX-plug is by fully upgrading your sound system. Its a shame that you didn't get it when you purchased your car for only 300$. Upgrading might cost about 400-600$. The upgrade adds alot thing in your car.
Also you can't only get the AUX-plug. The music-player with the AUX-plug also requires better speakers and two new tweeters in the front doors, and a "mode" button. As I said all of that will cost about 500$
And as a Volvo owner I can tell you that your car is not A2DP-profiled. And actually I want to note that when you speak with the handsfree, the sound comes from a seperate speaker that is fitted under your dashboard, not from the car's speakers.
Or you could try a FM-transferer. The quality is not that great but it does the job. Costs around 50-60$ 🙂
If you ask me about my opinion, id rather take the 600$ upgrade than 60$ FM-transferer because of the quality of the sound, but I'm an audiophile so I think that the transferer would work for you if you don't care too much about quality.