The basic transparent setup mode should work for you, the first thing to check is that your status LED is solid white.
https://www.quantumfiber.com/support/equipment/user-guides/c5500xk-smartnid.html
The pfSense Wan interface is plain IPv4 DHCP:
47870cfc-d952-42e3-89ad-82cf02c29f47-image.png
Centurylink and Quantum (at least) don't offer IPv6 connections in most areas. They do offer a very poor 6RD option to get v6 over the v4 connection.