IPv6 and DD-WRT custom DNS Setting

Okay, I I have a Linksys EA8500 with DD-WRT installed.  IPv6 is enabled with type set too "DHCPv6 with Prefix Delegation" and prefix length set to 64.  I also have Radvd enabled and DHCP6C and DHCP6S disabled.  I have an IPv6 assigned to my network and can connect to IPv6 websites.

my Issue I have right now is I do not know if this is the best setting to connect to IPv6 for Cox, additionally I'm trying to connect my IPv6 DNS to a custom DNS server I use for myself.  any recommendations to make changes to my setting to connect to the DNS?