You can use the Workflow reporting SMO's in the System folder. Create a listview and add the excel export control.
you can add then your own filters etc...
There is Show: (All) at the bottom left corner of the Designer, you can click the (All) link and enable the System checkbox, this will enable System category in the Designer.
It sounds like what you guys need is the K2 Odata Feed, I would avoid direct querying the K2 database.