I guess I should have double-checked this with my engineer.
Today, he sent me a response as to exactly why he used the .raw format:
I have come across this kind of a ‘glitch’ in sample playback maybe twice during all this time, so I just assumed .wav files were OK...and they very often do sound like they are playing back fine...but with this new information, I’m going back to saying that the Solaris needs .raw formatted sample data...just to be sure one get optimal results.The .wav format adds other info in data 'chunks' in between the audio data (such as sample rate, bit-lenght info, loop points, title etc.).
Also the audio doesn't need to be 16 bit - it can be 8, 16, 24 or 32 bit.
So even if you find a .wav format file that seems to work there is binary data played with the audio.
Depending on the sample material you may sometimes hear this as a short noise 'burst' or klick.
Even if it seems to work it actually doesn't.
Sorry ‘bout that!