I have found the manual online (see attachment) but it does not state the supported Bluetooth profiles - Bluetooth configuration in English starts on page 98.
This website seems to know the profiles however (found via Google):http://www.bassjunkies.com/audio/blaupunkt-new-jersey-mp68
Supported version: Bluetooth 2.0 with EDR
Supported profiles: A2DP (transmission of audio data), HFP (hands-free phone), PBAP (read access to phonebook)
Audio Streaming: Yes"
I have now found out that I should be able to select Bluetooth streaming as an audio source on my radio. That way I could hear the navigation system again and be able to speak hands free. Another consequence: I would have to listen to music and radio via my Galaxy phone in the future because only sounds coming from there would be played. My car radio would then only play the sounds streamed via Bluetooth.
I will try this out as soon as possible. Thanks for putting me on the right track and helping me realize that it's not an Android issue but rather a lack of features on my radio!