An implantable hearing prosthesis comprising an implantable upgrade module including a pre-processing unit configured to generate audio signals based on microphone information； and a implantable main module, physically separate from and electrically connected to the upgrade module. The implantable main module comprises a sound processing unit configured to generate stimulation information based on the audio signals received from the pre-processing unit, and a stimulator unit configured to generate stimulation signals based on the stimulation information. The hearing prosthesis also comprises a stimulation module configured to deliver the stimulation signals to a recipient.
