Three different schemes to amplify audio input, which one is correct?
None of those will allow you to pickup millivolt level signals.  

They will in fact reduce the level to some extent.

You can't use a resistor (or a couple of them like in a voltage divider) to amplify a signal.  

Amplification requires an amplifier.  This is an active device that takes a power input and a signal input and provides a stronger copy of the input as an output.



If you are working with anything but a dynamic microphone as your audio source, the level should be high enough to measure with an Arduino.  

I expect you are working with line levels as usually encountered with typical consumer audio devices.  The levels you've measured would be nonsensical in that setting.

A multimeter can't typically do much with an audio signal, especially the less expensive models that beginners usually start with.  I think inexperience and an inadequate tool have mislead you as to the signal level in your circuit.

Stop, back up, and hit google and search for circuits for interfacing an Arduino to an audio signal.  DO NOT look for your presumed solution (voltage divider) because it will lead you to the wrong thing.

There are numerous questions on this site alone about how to get audio into an Arduino.  Look for them.  Read up on "operational amplifiers" while you are at it.