Use at least 10awg wiring.  If you're not going audiophile stuff, and it sounds like you're not, try 10awg Romex.  It runs easy, is durable, and works well with up to a 40 amp draw.  The small increase in capacitance far out weighs the reduction in resistance and it takes a very well designed multistrand array, think Kimber or Cardas or the old Wasatch to have a more balanced sound than good ole' Romex solid core house wiring.