You seem to want 2 different things
CC can PULL (download) books using the Content server (the same place you can PUSH to the Library)
Calibre can PUSH books onto CC once you start the Wireless Device connection in CC
You just need to select the mode for what you want to do at the time.
I use WDC to update reading status on Calibre and to PULL updated versions of the books already in CC
I use The content server mode to browse my Calibre Library for new content I wish to have on my device