FileMaker Server *15* brought back the ability to easily install FMS on a Mac running OSX Server by associating the FMS web services to different non-standard ports (and there are multiple reasons for running "Server.app" that I won't go into here...)
FileMaker Server *16* will not install on a Mac running OSX Server because it complains that apache is in use.
The recommended solution for this is to trash Server.app to install FMS 16.
This is an unacceptable solution for a number of reasons (I will be happy to go into them if necessary.)
Please bring back the ability to install FMS on a Mac running OS X Server!