Here is a way to get access to your F5 and F6 keys, and any other functions keys you want, as Hotkeys. It uses the keyboard remapping application Karabiner Elements.
1) In keyboard preferences, click "Use F1, F2, etc. as standard function keys"
2) Download and install Karabiner Elements. https://github.com/tekezo/Karabiner-Elements
The main application Karabiner does not yet have a version for Sierra. Karabiner Elements provides some of its functionality, including control of the Function keys. If you are running an earlier OS, you might find an older K