Routing +12V and -12V for audio opamps?
Dedicating a layer for grounding is not necessary in audio.  Ground planes are an RF technique. At audio frequencies, you're not worried about effects like currents leaking across the epoxy substrate.

I just built a dual-supply (+/- 15V) audio board with four op-amp IC's, like yours.

(It was originally going to be a single layer design with a few jumpers, but then I decided to go with a manufacturer that makes two-sided, so I rerouted it.)

The +/- 15 power rails are strictly in the top copper, and the bottom contains the ground traces (not pours) and signals. Thus I have no jumpers, and no vias that exist just for the purpose of routing a network to the opposite side. (But not that it would matter! A signal, power or ground trace having to go to the other side and back has no effect at DC or audio frequencies. Stray inductances of of vias and such are another RF consideration.)

There is a small exception to the signals being on the bottom: late in the design I decided to add a stereo/mono switch, and some of the traces for that ended up in the top copper.

The finished unit is very quiet, and the sound quality is terrific. 

If you have a good, dual-voltage power supply, quiet, distortion-free audio mostly boils down to the choice of op-amps more than anything else (I used NE5532's from ON Semiconductor), avoiding extremes like excessively low or unnecessarily high input impedances, and good supply bypassing.