Andrew this video of Nina's might help you out some...
http://www.youtube.com/watch?v=Q0Kyg0FXXD0

I'm not sure I understand the situation. The tempo of the music should not dictate what dynamic levels are possible...Is that what you're experiencing, though?

Now Micron, I've got to comment:
"So practise until you can play it well and flowingly at speed. With beautiful phrasing that matches that melody, it will provide a beautiful sparkle, without being like the bum of the flightlebee."

Well turned

I think that the importance of the Nina instructions should be in her attempts to get some wayward students to open up the embouchure hole a bit more. A considerable amount of volume can be increased if they are rolling too far back and this can be avery common issue. Then there's the issue of the type of flute. Some flutes/head joints and the like are simply easier to play with more volume than others. If this person is playing on a quieter flute, no sense in forcing it. The projection will cut through only with a clear, pure & focused tone.

Of course (as suggested) all IS lost if it's out of tune or if there is no smoothness to this obligato because then it is truly the bumble of the flutterbee.

I find there is nothing more confusing than the theories about correct breathing, air column support, diaphragm/abdominal/intercostal muscles, not counting body/head positions, arm position, hand positions, embouchure.. oh well, we could write several books on the different approaches to the embouchure.

I have three different teachers: one for flute and two for sing. They have, of course three different approaches in this matter. In singing, they are quite opposite!. I believe I am not told two opposite theories about breathing for the flute...because I have just one teacher.

So far I am so confused that I tend to develop my own practise; I listen to everything I am told to do, but the moment will come when I can decide on my own way.

Probably all these theories have a part that is true and a part that is mere myth. As almost everything in life.

Or it could be that I am a little on the negative side today, it a side effect of my approaching audition...

<Added>

OOPS! it a side effect = a side effect

Sorry Andrew. I only caught the beginning of it before posting it. I have watched some of Nina's other videos in which I found to be helpful, so I posted this one.

I just noticed that I gave you the wrong video of hers, I mean to give you this one, in which I DO find helpful and I DO agree with.

http://www.youtube.com/watch?v=O0XfoandDjk

Thaks Kara for updating your link.
"Support" is relatively important to dynamics but not so as important as what Nina is saying about not rolling in to far.

If I were conducting this piece, I din't think that I would go faster than 88BPM. I think that my concept of the hymn tune would be about that fast or even slower. "BUT" I've heard other directors and organists play other pieces wwaayy too fast and as a mere flutist, I would be obliged to try to follow them. I'd practice slowly for good tone, fingers and tuning. Then work up the tempo.