I think I know the answer to this

But, Is it possible to have a key, say with 6 fields, and to change say the third field to be decending and leave the others to acending. Thanks.

Not automatically BUT you could write code behind the data field to calculate the inverse of the value!

Humm… I can read your mind… you are thinking… NO [:D] But you can use Excel for this purpose. Is it possible in your case?