"I think of usability as a component of user experience, rather than as a separate thing that can vary completely independently. "
I think this statement is key to this discussion.
I too believe that usability is part of the grander picture that is the overall user experience. That is, I believe it is not about finding a balance between usability and user experience, but instead to find the right balance between all the elements that create the user experience.
I.e. finding the right balance between aesthetics, usability, and technology etc for any given project creates a good user experience.