I have an issue with Impose on a customers Mac Pro with OS 10.11 and Acrobat Pro DC preinstalled.
After installing Impose (Acrobat X. PitStop 12) there are both Acrobat versions running on Mac.
If i set OS X to open PDF files with Acrobat X as default, it works well.
I doubleclick an PDF file and Acrobat X is opening that file, and i can use PitStop.
Now, in Command Workstation, i "preview" a document and "edit in Acrobat..." - it is opend always in Acrobat DC (without PitStop...).

What i had already done:
Try different Versions of CWS ( 5.7; 5.8)
Deinstall CWS (with software uninstaller- discard all settings).
Reinstall latest CWS.
Is there someone who get's an idea?