I didn't run across any documentation on an eConnect proc that I found very useful while working with some eConnect integrations recently. I needed to update, not insert, a SOP Header record after adjusting some line item prices through code.
I found that using taSopHdrRecalc worked great for this. The schema is basically the same as the taSopHdrIvcInsert so you can consult that schema reference in the eConnect Help when working with this proc.
If you weren't already aware, Steve Gray has posted the eConnect Help Online here.