leenia, sophocleese described those cheek muscles really well. My teacher calls them "snout muscles", and at first it was hard for me to even isolate them to feel any control over moving them. I haven't even kept up on that practice (tsk, tsk). I can look at my teacher's face when she lifts them, and see the skin either side of her nose, below her eyes, go up quite a bit! She can isolate and just lift that part of her face to add a brighter sound, something you can do to add variety to the sound of what you are singing... bring out a certain phrase with the contrast of brightness, or maybe sing a repetitive part differently by adding brightness sometimes.

Rather than pushing air against your vocal cords to get volume, you will save your voice and have a clearer tone if you relax and float your voice on more air. It may seem like the volume is softer, but your voice can actually carry over the instrument more if you have enough breath support to really flood the sound with air. This is hard to read about instead of being able to see it demonstrated in person.

Alice