Close. What happens when you sum the outputs of two devices is that the signals they have in common (the real data or music) is summed (x2) while the random signals (noise) is cancelled. This is because the real signals occur at the same time in the same phase while the noise on one DAC is likely to be slightly different from the noise on the other. When you sum, the noises cancel and the real data sums.
Result is improved SNR.
Result is improved SNR.