[jyl]

Source A would be the original, period correct car stereo head unit in the original location in the dash.

Source B would be a modern head unit with Car Play, GPS nav, and all the goodies, mounted NOT in the dash.

Both use the same amplifiers and speakers.

The idea would be you use Source A (with Source B hidden away) when alone and enjoying the pure simple driving experience, and switch to Source B when on a family roadtrip with the spouse and kids whining up a storm. A single touch of a factory-looking rocker or button should instantly switch between sources.