System including a CIC hearing aid that is constructed from a first universal part containing microphone, amplifier and loudspeaker and a second part that is adapted to the auditory canal of the patient. The hearing aid is of a digitally programmable design. The programming is carried out by way of a cable. Since a connection to the first part is not easy to make on account of lack of space, it is proposed to use an auxiliary part that replaces the first part and is used for establishing the desired amplifier characteristics. The desired amplifier characteristics obtained in this way are transmitted to the first part to be used by the patient by contacts that are accessible when the aid is removed from the ear.