I have discussed David's Tinnitus Mix with a neuro researcher who is a friend of a friend. He does not specifically deal with tinnitus but is well versed in it and other ailments of the ear because many of the trials and research revolves around issues that involves tinnitus. I had a theory on why it may possibly work but I didn't disclose my thoughts until the researcher gave his opinion.
He believes, without knowing too much about the Tinnitus Mix itself or anything to do with harmonics and frequencies, that the Tinnitus Mix might provide relief because of its erratic and unpredictable pattern of sounds. When we sleep, it is believed that we can still subconsciously hear tinnitus, I guess depending on the type. Tinnitus while sleeping perpetuates the feedback loop and continues to stress our nervous system and David's Tinnitus Mix interrupts/masks the sound of tinnitus with erratic noises that are not in any discernible pattern. He explained that even masking with white noise won't have the same effect because your brain will recognize the white noise and it is predictable, as are waves and rainforest sounds, etc.
I was thinking along the same lines and was really surprised when he gave his opinion. There is a video on YouTube, 4 hours of neuromodulation for tinnitus, and it seems to be practical for many people as well. I guess it uses the same principle where the sounds are erratic and unpredictable in a sense so while masking the tinnitus it breaks the feedback loop that is commonly discussed. If I'm not mistaken, ACRN uses a similar principle so it's no wonder that the Tinnitus Mix might actually work. I will try and report back.