Which component must every System 6000 have?

The mainframe is an essential component of every System 6000, as it serves as the central processing unit that houses the system's operating software and integrates all other components. Without the mainframe, the entire system would be non-functional, as there would be no platform to run the audio processing algorithms or manage the underlying architecture. The mainframe allows for the connection and management of various modules and input/output cards, which are necessary for signal processing, but these components cannot operate independently without the mainframe's capabilities.

While the other components, such as the remote CPU, TC Icon, and input/output card, enhance functionality and user interface, they are optional additions that provide specific features or controls rather than being fundamental to the operation of the System 6000 itself. Thus, the mainframe is the indispensable building block of the entire system architecture.