If you want to proceed further backwards in time, there are still three great resources, but for the great majority without indexes: catasto onciario (in archives, mostly in Naples and municipalities), parish books of deaths, baptisms and weddings (mostly in parish churches, some in central church archives) and notary acts (in state archives).
Notary acts are usually the last step, since searching through them is very slow. For most of these the keepers of the resources (archives, municipalities, parishes) must be contacted to check the existence of records and obtain permission to make research. This means patience is ABSOLUTELY NECESSARY.
The Onciario is a great resource, since a kind of "census" was requested, listing all the possessions to be taxed but also, what is most interesting for the genealogist, the composition of all the families, with names and ages of all the members. Click on the link below to see if the years you need are available for your municipality and province
If the catasto is available in archives, list all the families with the surname you are researching (they might be connected) and request photocopies from the archive for your families. The cost will depend on the numbers of inhabitants inthe place, and on the number of families bearing the researched surnames. Archives in Italy may apply different rules.