There are a few things to consider when purchasing an audio amplifier for a HT subwoofer. The first is the power supply. A good rule of thumb is to get an amplifier that can handle at least 50 watts RMS. This will allow the subwoofer to power itself, and will also allow the amplifier to handle high-volume music without clipping. Another important factor to consider is the type of amplifier. Some amplifiers are better at handling high-volume music than others. For example, a tube amplifier may be better at handling high volumes than a transistor amplifier. Finally, it is important to choose an amplifier that is compatible with the subwoofer. This means that the amplifier must be able to power the subwoofer and the subwoofer must be compatible with the amplifier.