There are specific types of amplifiers, such as bi-directional units, that work with digital cable boxes. Other units that are not built to handle speeds of 1 GHz or more cannot be used to help amplify the signal for a digital cable box.
Bi-directional amplifiers are special units that help boost the signal of a cable box. These units are mounted inside of a house and feed the box signal to the cable box mounted outside. These units are often included as a premium in certain cable subscriptions, but can also be purchased from amplifier dealers such as cableTVamps.
Other types of cable signal amplifiers include active return path, return path and forward path units.