Question Help wiring switching audio

[FreedomCookie]

I think I know how to do this, but I just wanna make sure before I go ahead and start. I'm planning on wiring in a headphone/amp switching circuit to my handheld (a unit running RetroPie), which is on a Raspberry Pi B+.

Using this TRS jack as an example, I'm pretty sure I need to wire

• Terminal 1 to ground (pin PP6 will be taken by the monitor's ground, should I just connect this to a ground in GPIO?)
  
• Terminal 2 to left audio souce (pin PP25 on RPi)
  
• Terminal 3 to right audio source (pin PP26 on RPi)
• Terminal 4 to left amplifier
• Terminal 5 to right amplifier

Please confirm or correct me on anything. Last couple of questions:

• Is there a small board that comes already wired with amps and jack so I can do less work?
• Does anyone know where I can get some cheap but half-decent amps? Otherwise I may just tear into some old electronics.
• How do I add volume control? Do I have to go through GPIO?