Instead of using a preset channel, try using autoplay.
I have mine set up as follows
-For each Object-XAudio2: Autoplay file "sound.wav"(Loop) at Object
-XAudio2: Set channel XAudio2.LastChannel volume to 1dB
I am thinking it might come down to being limited to 1 channel per object, so while this works, if you have 64 shore objects....you are going to run out of channels.
Alternatively, you could try attaching the sound to the ocean/water body beyond the shore objects, it generates the the sound from the object as a whole instead of one point, then this might work for you. You will need to do some experimentation to see what works for you.