Analog Audio Signal over dedicated Ethernet/Twisted Pair Cable
I think a good question to ask here is: what kind of audio signal?

If you can spare e.g. an Opamp per channel and end, plus the power for that, and a terminating relatively low resistor (e.g. 120 Ω, 47Ω, or even less), then you'd waste power, but you'd get a very stable transmission.


  
  Audio Right In 
  Audio Left In 
  Audio Ground In
  Audio Right Out 
  Audio Left Out 
  Audio Ground Out 
  


Don't do that – your twisted pair cable is meant for differential pairs. So, instead of transmitting ground (which is just a recipe for all kinds of avoidable hum and DC currents), convert your single-ended audio on the transmitting side into a differential one, and transfer that on a twisted pair (blue / blue-white, and so on):


Blue: left -> +
BlueWhite: left -> -
Brown: right -> +
BrownWhite: right -> -
Green: left &lt;- +
GreenWhite: left &lt;- -
Orange: right &lt;- +
OrangeWhite: right &lt;- -


Converting from single-ended to differential can be done using inverting op-amp circuitry, or opamps with differential output, or dedicated differential line driver ICs, or signal transformers.


  
  12 V + 
  12 V -
  


Nah. Ethernet cable's not a good conductor of current, so you'd avoid this. 

Also, if you use a signal transformer on the end, you can just use the center tap to impose DC over your differential audio signal, and can avoid having dedicated power pairs. That's how Power-over-Ethernet works!