https://www.parts-express.com/dayton-audio-dsp-408-4x8-dsp-digital-signal-processor-for-home-and-car-audio--230-500
https://www.parts-express.com/dayton-audio-dsp-bt40-bluetooth-data-and-streaming-usb-interface-for-dsp-408--230-502
Use these to bypass headunit and connect to DSP via Bluetooth.