Update 1: El Capitan follow the same procedures, but you may have some difficulty with the compile/install, see the section at the bottom for specific help with El Capitan.
Update 2: Same procedures for High Sierra. Only complication was Slow Files (which is documented in the troubleshooting section).
Installing X-Sendfile for Apache is actually quite simple. However, I could find very little documentation out there. Here's my attempt to help out. In order to proceeed, you'll need:
- XCode installed including the "command line tools" (http://railsapps.github.io/xcode-command-line-tools.html)
- Source code (https://github.com/nmaier/mod_xsendfile)