@pfBug:
Now, what I want to do is use a different router than my ISP provided. I don't want to use the new router in AP mode because it locks out features that I specifically bought it for. I think I can set the ISP's Modem/Router to bridge mode and then connect my new router to it, but again, this is based on my minimal understanding at this point.
If you set it to bridge mode, AFAIK it does become a simple modem. You then just run ethernet CAT 5 from your (now simple) DSL modem to your WAN pfSense port. It should already have one RJ11 jack for the telco connection and one RJ45 jack for the ethernet connection.
I'm not sure I see how or what features would be used if you set it to bridge mode. The modem just disappears and becomes part of the furniture :)