Hi,
It depends of your needs, you can buy an integrated pure BT chip that communicates with the MCU and sends it the data packets so it can reproduce the sound, or you could buy the cheap modules with an analog output which you can directly connect to the amplifier. There might be single ICs that do so (not a PCB with connectors and a circuit) but you should research for availability and layout, for example the 2,4GHz antenna.
I have seen portable amplifiers with the bluetooth module (a pcb with an IC and circuitry) soldered to the main PCB of the amplifier, you would not be the first to do that.