I want to automatically switch audio sources in my car using a VOX like feature. I would like to make it a smooth switch (no pops)?

A CD4053 can be used to switch line level stereo audio. Use a bipolar (+5/-5 volt) supply to eliminate the need for caps on the inputs and outputs. There won't be any loud pops as long as there isn't a DC offset on the inputs.

Use a 10K ohm resistor to ground on the inputs to keep DC offset under control.

The LM 13600/LM13700 has always been my goto for this. It may be overkill, but each input can have its own gain-control and an RC network on the Iabc input means that the gain-change can be slow enough to avoid any DC pops. That and the fact that it's an (admittedly enhanced) op-amp means that common-mode means no hum loops.

I know this is the least hack happy answer. I had the same goal as you at one time. But I used a cheap mx44s by rolls.It gives you the ability to make the GPS much louder that the music or the opposite.

I actually had 4 inputs. It had voltage regulation on board and could take variable voltage from 9-15 volts DC (great for auto use). I know its sort of lame but for 40 bucks it was cheaper than any home build application I could think up for what I wanted.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.