JayGilb
Major Contributor
I would just make both pours the GND net. There's no reason to make a power plane for the +12V since its just powering 3 relays. There could also be a potential problem if the +12V power supply is noisy, it could induce noise into the audio traces if it surrounds all of those traces. Remember if there are landlocked areas which won't pour, use vias from the top to the bottom layer so this doesn't happen.
Good advice on not creating a V+ power plane.