There are some enhancements in K2 version 2.0 that allow for certain double-sided CIP applications that didn't generally work with the standard CIP plugin for the Harlequin RIP. Read about that in the release notes.
The gist of it is, you output impositions as sides instead of all of the imposed flats being packed into a single PDF job. Then, the CIP plugin names them in a way that lets you see what each sheet and side are at the press console.
This PDF Output control in the imposition dialog lets you change beween Job, Side, Signature, or Web. Job is the old default and didn't work well with the CIP plugin. So try "Side".
You can get more detail here. Otherwise, scroll down for the CIP output plugin manual.