For audio processing, the Model 990 employs a 24-bit Cirrus Logic CS-49400 Crystal processor, and 192 kHz/24-bit Analog Devices digital-to-analog converters for each individual channel. The unit features decoding and processing of every major surround sound format in existence today, including Dolby Digital EX, DTS-ES, DTS-96/24, DTS Neo:6, and even a fully adjustable version of Dolby ProLogic IIx processing. A pair of Analog Devices Asynchronous Sample Rate converters are used to remaster PCM sources to 192 kHz/24-bit audio for improved reproduction of CDs, particularly in the upper frequency range. There are both Pure Analog and Pure Digital modes to prevent deterioration of sound due to unwanted conversion between the analog and digital domains.

The Model 990 is designed to be both firmware and software upgradeable, allowing for inclusion of future surround processing schemes and additional features. There are both USB and RS-232 ports on the unit's rear panel, allowing for a convenient and simple means of connecting a personal computer for future upgrades. The USB port can also be used as an audio source connection, allowing the processor to play PCM audio files streamed from a computer.