I have no doubt audio signals can have profound impacts, but it is different for everyone. No sound makes me happier then experiencing a 23 minute live perofrmance of "You make me realize" by "My Bloody Valentine", but this is just me, and something in me that connects to this.
I am sure we all believe that sound is capable of some real amazing things otherwise it would be difficult to explain why we are involved in this wonderfull Axoloti environment. But everyones goals are different because we all are wired a little differently with strengths and weaknesses that can be manipulated very well if you know what you are doing.
Yes we need to be mindful of those with epilepsy, its a horrible disorder, and we need to protect the pregnant, young and ealderly from the experiments.
There are people already out there who know how to take advantage of the mind, in fact Darren Brown shows how a random citezen can be hypnotized without even knowing its happening, and then commit a crime. It is the power of the mind and there are people out there that know how to take advantage of it all ready.
I know the post is somewhat going off topic, but it is a very interesting debate, definately areas with lots of room to experiment. Music and sound will always have room to question such, in history we had the "devils tritone" people were killed for using it. Because it invoked tones that were at the time considered unpleasant. Then we have the scales and cords themselves, the blues is played with certain notes to invoke a certain tone in the music. This may be considered different to the idea of dangerous freq, but I don't think it is. Christain Evangilists have musical specialists use songs with certain beat patterns, certain tones that change throughout the event that change the viewers activity, pace of the heart beat, to simulate a form of exhaustion, so that towards the end very specific musical tones are used so that the combination of the veiwers physical state combined with their desire to experience something spiritual is almost garaunteed. These techinques are very well documented in psychiatry and are used to manipulate us.
Once again, its all about the power of the mind, given the right environment we can believe anything is happening to us.