PBox on existing LAN with RPi b

Hi everyone, this is my first post, so correct me if i make mistakes.

I need help with my setup, which is this:

i have installed PBox on my Raspberry Pi and as an AP it's working perfectly. but i would like to make it work in my existing lan, basically acting as a dhcp client to my main router but dns server, so when i type in "piratebox.lan" i go to the local page, but if i type anything else the dns request is sent to (for example) google's 8.8.8.8

to this point i modified the config files so that the AP mode is disabled and eth0 is the selected interface. so if i type in a browser "internal ip/content" i access the main page (but the file upload isn't working). Now if i set the dns server of my main router to the RPi's ip, the redirection works but the landing page (piratebox.lan/content) is not reachable (as is every other page, it predictably says "dns not resolved" ).

I tried messing with the dnsmasq, hosts and resolv config files, but didn't manage to understand which is the effectively used file (/etc/dnsmasq.conf or /opt/piratebox/.../dnsmasq_generated.conf and so on), so after many hours of tinkering, i gave up and resolved to ask for help here.

Thank you

Diego