If iTunes tells you it cannot locate the file, that means that either the file has been moved, renamed or deleted since you added it to your iTunes Library. So this leads to the question "what are you, or one of your programmes doing to the file after you add it to iTunes?"
I assume that your turntable is creating the file as a .wav file, as well as choosing the location for that file it creates, leaving you with little choice in the matter. If this is what happens, and you then add the song to your iTunes Library (or the turntable's programme does it for you) and you subsequently move, or rename the file, that's why iTunes can no longer play the song.
If that is what is happening, then either move or rename the file before adding it your Library, or follow the iTunes prompts to locate the file in its new location (or by its new name). Once added, don't edit the file. Instead, edit the song, in your iTunes Library.