New answers tagged a2dp
Technically it is possible with most Bluetooth Android phones but you would have to root your device and find a ROM with source code like CyanogenMod and rewrite the Bluetooth driver.
Unfortunately there is still no bluetooth server implementation available for android devices. The connect as "music player" part of your question could be realized via WiFi, using the SoundSeeder Music Player app (soundseeder.com or forum.xda-developers.com/showthread.php?t=2392672 You need to connect your devices via "WiFi direct" or the portable hotspot ...
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