Obviously $300 is not worth going to court over.
Don't go back because chances are they don't have the capacity/skills to redeem themselves (I would not think that it is hard to plug in speakers after installing them) and its more likeley they will have the shits and probably do burnouts in your car or something vindictive.
People here are recommending someone else so just take it to him and don't go JB again.
You will be so much happier picking the car up with everything working from the guy that is being recommedned (Chris) rather than having to drive to JB for the next few weeks getting them to fix their own mistakes (as chanes are they will not get it right first, second or third attempt).