The invention relates to apparatus and methods for upgrading a set top terminal for use with a cable television program delivery system. A hardware upgrade or expansion card is connected to a set top terminal to enhance the functionality of the set top terminal and to allow the set top terminal to receive digital audio programs. The hardware upgrade includes audio signal processing circuitry such as a tuner, demodulator, demultiplexor, decryptor, and decompressor. A microprocessor in the hardware upgrade enables the upgrade to accept subscriber inputs so as to select a particular digital audio program for listening. Subscriber inputs may be generated from a remote control and a menu system of the set top terminal.