I have two Aurora 16's and two AES16e cards. How should I clock them together?

Presuming that your studio does not have a master clock, there are two typical clocking methods used in this situation:

1.) Card as Master
Connect the Lynx CBL-ICC cable from the clock out pins on card #1 to the clock in pins on card #2
In the Lynx Mixer, set the PREFERRED CLOCK SOURCE for AES16e card #1 to "Internal"
Set the PREFERRED CLOCK SOURCE for AES16e card #2 to "Header" (if the ICC cable is connected correctly, you should see a sample rate next to "header" under preferred clock source in the Lynx Mixer)
Set the SYNC SOURCE for both Auroras to "AES A"
Power Cycle the Auroras with the front panel power switch to save this state. 

With this clocking method, the system will respond automatically when you change sample rate in your audio software. 

2.) Aurora as Master
Connect a wordclock cable from the Aurora #1 WORDCLOCK OUT, to the Aurora #2 WORDCLOCK IN
Set the SYNC SOURCE on Aurora #1 to "INT"
Set the SYNC SOURCE on Aurora #2 to "EXT"
Power Cycle the Auroras with the front panel power switch to save this state. 
In the Lynx Mixer, set the PREFERRED CLOCK SOURCE on both AES16e cards to "Digital In 1"

With this clocking method, you must manually set the SAMPLE RATE on Aurora #1 to match your project rate in your audio software.