Just a quick design. This is an enclosure for a cheap bluetooth module, with some space to tuck in the cables. Holes for 3.5 mm stereo jack output and 5.5 mm power supply socket. Extra hole for passthrough of a power supply cable.

Update: Second hole for 3.5mm stereo jack added, to enable AUX input (depends on module, had to solder extra wires but it works)