You don't need the static NAT (unless internet people contact this server for resolving your domain) and the outside ACL permitting UDP/53. Check your log when you do a DNS query and see if there is anything in there (post it if you like). Also x2 the ACL applied on the inside interface or post it if you have any doubts. Finally check the DNS inspection. The default is 512 which can be too small. Increase it to something like 1024.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...