How to setup DNS going upstream?

For proper stats to be displayed on the dashboard you have to see if its possible to configure the Amahi DHCP service to push the Pi-hole IP address to its clients for DNS resolution (methode 1 and also the link that was posted in the first reply on top):

And activate Conditional forwarding so Pi-hole can lookup all names that are local to your network against the Amahi DNS service.

EDIT: And test with nslookup eg:

nslookup <HOSTNAME_LOCAL_NETWORK> <AMAHI_IP>

&

nslookup <HOSTNAME_LOCAL_NETWORK> <PIHOLE_IP>