I only ever used Wave 1 as I found that did all I needed at the time. My main difficulty in achieving a controlled, conscious-exit projection was achieving the Focus 12 state. Once I’d reached this state then everything would roll more or less by itself from there.
I would say that Focus 10 and Focus 12 of the Monroe model are the essential pre-requisite states. In my opinion the rest of the series are a bit of a commercial exercise. If you can achieve a definite Focus 12 then you should be able to reach Focus 21 with little difficulty. From there the non-physical world’s your oyster, so to speak. Any kind of CD going off in your ears wouldn’t make any difference as you wouldn’t be physical to hear it. Unless you switched to an overlay experience but what’s the point? Then you’d be listening to a CD so called taking you to a place you’d be at already.
So if I were you I’d concentrate more on the beginning CDs and try to reach a definite Focus 12 and you should find the experience takes on a life of its own.