I would not expect any interference. I recently ran a test using a 12/4 cable (four 12 AWG wires encased in a single cable). I use two of the conductors for RLC measurement purposes and playing test tones. I used a B&K model 885 to measure the RLC parameters. I used a Rat shack multimeter to measure the frequency of the test tones (connected directly to the wire), and a BOSS tuner to measure a concert A from the speakers. All of this was repeated three times. The first time the two unused conductors were doing nothing. The second time the two conductors were powering a 500 watt photo lamp. The third time, the two conductors were playing pink noise to achieve 75 dB 1 meter from the speakers.
In each of the two tests, there were no observable (or audible) differences in measured parameters compared to the baseline test.
I would however, recommend a larger gauge wire for the speakers, say 12 if you can afford and fit it. 14 AWG minimum.