Outlining in DTPO

I would like to have an outlining program that has expandable/collapsable fields within the document and works well with DTPO. OmniOutliner seems like it might be pretty good. Do you have any experience using that software with DT, or other outlining software with DT? Thanks for any feedback.

Any software supporting Quick Look and Spotlight is fine for DT. You might also give Opal a try.