Is there any reason you want wireless? Bluetooth audio is a disaster, AFAIK. You don't want to use it for music. Just go wired, the ether is too cramped already.

There aren't many choices of cheap hackable A2DP receivers if you were somehow looking for one. Not all headphone chips are programmed to run at slightly under 3.3V on VBAT pins so to protect the supposed battery, with no means to reprogram for lower voltages, officially or not.

There are alternatives, but being able to use an external amplified speaker and also move around easily would be nice. Maybe it's not feasible yet.