What sorts of things will the CMS need to do?
Blogs: Keeping students and staff up to date of of news and events
Forums: Students asking staff and fellow students for help with whatever
Wiki perhaps: for subject info pages, pages with exercises, exam timetables, etc, etc
Download/file management: storing of course syallbus files, copies of past exam papers, subject handouts, etc
One option would be to choose an app for each purpose and "bridge" them eg wordpress and phpbb can be "bridged" so that logging into one logs you into the other