Common when wiring audio matrices like a DBX, there are Phoenix connectors for audio input. You might need to build adapter cables to connect RCA output source devices to the Input of the DBX. Know that a DBX used in commercial applications are most always set for Mono. Which means, the Left and Right signals are summed internally in the DBX so a combined mono output is then sent out to the amplifier channel.
Here is a video tutorial that gives all the details on how to make such a cable.
Typical Stereo minijack wiring diagram
Example of minijack to balanced phoenix connector. Ensure your pinout on phoenix is same...DBX uses the middle as the +
Example of summing R and L channels to one phoenix channel
To sum a stereo pair to a mono signal it is recommended to terminate (2) 1K ohm resistors to the Left and Right channels and then tie them together. Solder one side of the first resistor to the left channel followed by soldering one side of the second resistor to the right channel. Next, connect the bare wire of the left channel to the bare wire of the right channel, this is the ground. Finally, connect the two resister ends together and this will be “+” of the mono signal. Shrink tubing is recommended to protect the soldered connections to the resistors.