Hi Eric!
As far as I know, a complete ArtRage 6 manual doesn't exist. I agree with you that especially the Brush Designer of the Custom Brush isn't easy to understand, but by testing the adjustments one can find out what they do, with a little patience. And if you find some brush settings you like, you can save them as presets for a new brush. That's the way I work with it. sometimes I am testing around, creating brushes by the way. Other days I paint with the results of this testings.
But maybe this Youtube video may help you (I didn't watch the whole video - so without warranty).
Edit: Here is also another video.