The secret, is just to practice. Practice playing overtones. It really helps you in the long run, since altissimo notes are just overtones. Yous set up shouldn't have anything to do with being able to play overtones, though I have noticed that it's sometimes easier to play them when ou play on a new reed, while it's still sorta hard. As for your embrochure, don't change it! If you're changing it, you're doing it wrong. It should stay the same. However, you do have to change the position of your tounge and throat. Your tounge needs to be arched high, close to the roof of your mouth, using fast moving, cold air. I can't tell ya how to change your throat. It's different for everybody. Even it it wasn't, I still counld'nt describe how you hold your throat. Anyway, try this and see. Main thing is, is that its just gonna take some time and work. But you'll get it!