It is true that an Android phone is uniquely A2DPsource devices.
Unfortunately, your first case cannot be realized if you decide to rely on a profile A2DPfor audio streaming, since Android does not implement the required callbacks that BlueZ ads are supposed to handle when the remote device wants to transfer audio to your phone.
The second use case is possible, given that you have a bluetooth-compatible PC and some amazing applications that will decode and direct the sound from the Bluetooth stack to the speakers. I was able to reproduce this use case with PulseAudioand pulseaudio-module-bluetoothon Ubuntu 12.10.
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EDIT:
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