I confirmed with NetDog
that my CMTS was IPv6 enabled before beginning this adventure but alas what should work what that actually happens are sometimes two entirely different things LOL. Regardless, I should try that and see what happens.
Though I did note in the thread you pointed me to, your IPv6 IP shown was a 2001: address. If the PD provided 2601: address is the source of the issue, I may very well be able to connect the modem direct to my computer and get IPv6 connectivity and then turn around and still not get it to work with pfSense.