Does playing music during sleep actually suppress rather than rouse the brain?
This is a very interesting but difficult to answer question. That is because scientists are still debating about the various stages of consciousness. As it stands, there is evidence that people can learn even though they are asleep indicating that it is likely that sensory channels are open and information is being processed even when asleep. That likely means the brain is behaving as if it were awake at certain times during sleep. In this article they interpret the lack of blood flow seen by fMRI as less active which is mostly correct. Playing audio during REM is a tricky question because as you know dreaming does not require sensory input so that channel(hearing) may be free to receive information although your guess may also be true if if the music was loud enough to interfere with other cognitive processes.