just use stereo phono to 3.5mm stereo jack connected to the aux in on the rear of centre console.
perhaps opening up the rear centre console and redirecting the rca connectors with an extension cable to wherever you need is the simplest, cheapest option.
you could also get one of those adaptors that use a radio frequency, they often have stereo inputs too.
like this one, yes its on Amazon, im sure I will get in trouble for posting links one day, but this is for an example.
Adds audio input, usb storage, sdcard, 2 additional USB charging ports, a remote and controls.
https://www.amazon.co.uk/Clydek-Bluetooth-Transmitter-Wireless-Charging/dp/B08DCTCZ2K/ref=sr_1_9?c=ts&keywords=Car+Audio+FM+Transmitters&qid=1649015535&s=electronics&sr=1-9&ts_id=528666031