Many people ask how to build one. Let me tell you it is not very easy.
The device consists of two parts a D2B audio controller and a Raspberry PI which handles the Bluetooth streaming. The latest version of the unit user Raspberry PI Zero – the regular, not WiFi version.
The two boards connect together via 40 pin header. The D2B unit receives audio via I2S protocol from the Rapsberry PI. The two units also communicate via serial interface. The Raspberry PI is powered by the D2B audio unit. The D2B audio unit also can reset the Raspberry PI board if it is not responding to serial commands.
Here is the schematics of the D2B unit. Jaguar D2B board
The micro-controller is Cypress PSOC4 4100 series. Here is the firmware it is running.
The Gerber files that one can use to make the PCB.
Instructions how to built the software for the Raspberry PI board.
You would need a micro-sd card for the Raspberry PI and a Bluetooth USB dongle (The ones marked with CSR 4.0 work fine)