Choose the cable that connects the Mainframe to the Remote CPU.

The correct choice for connecting the Mainframe to the Remote CPU in the TC Electronic System 6000 is the X-coupled Ethernet Cable. This specific type of Ethernet cable is designed to facilitate the high-speed communication required between the Mainframe and Remote CPU, ensuring that audio data and other signals are transmitted efficiently with minimal latency.

Using a standard Ethernet cable may not support the specific protocol or bandwidth required for the seamless operation of the System 6000. USB cables, while useful for many purposes, do not typically provide the necessary networking capabilities in this context, and FireWire cables, although capable of high-speed data transfer, are not the standard for connecting components in this particular system architecture.

Thus, the X-coupled Ethernet Cable stands out as the appropriate choice for establishing the required connection to meet the operational demands of the TC Electronic System 6000.