Not true. It uses a hit file instead called psionicmelee_Hit.ogg which is located at sound\ogg\powers. However, using pggviewer pro, it does not show up...in fact none of the powers for that particular pool power group shows up. However, I am willing that if I modified that file and placed it in the Data folder under that destination, it would work.
Having said that, the sound can be changed, however, what it will also affect is the Hit effect for Project Will and Wall of Force. So unless you don't use those two powers, it can be done. Your idea is the optimal direction we would want to take, but to do that the Devs would have to write new code which means they probably wouldn't be talking this any time soon. However, in the mean time, as long as you don't use Project Will and Wall of Force, I can cook you something up that will give you the same effect you desire.