Holderlin- I agree with Jadem6, but I would consider at least two dedicated, continuous circuits (including the ground wires) from the junction box to the audio room outlets - three if you were running monoblocks. I would also thoroughly inspect the existing ground rod and associated connections. If advantageous, look into the addition of another ground rod (local codes may preclude the separation of the audio circuit grounding to a separate ground rod).
Good luck.
Good luck.