Hi Allegra,
I apologize if this is something you have and were trying to do things differently, but our iWave setup/integration has a utility specifically for pulling all the information iWave needs, you just add a list to it. When you run the utility it even automatically uploads it to iWave, you still have to go into iWave and tell it to screen the pull (it doesn't just automatically spend your credits). If you don't have the utility but do have the iWave integration with Tess it might just be that you need to be given access to it in the security module.
If I misunderstood and that isn't quite what you are looking for you can also create custom output set parameters. We have output elements for largest gift and number of contributions that we wrote. I can try to share if you'd like, but the KC Opera is part of a consortium so our setup might not translate to yours.
I hope that helps!