Q. AuthentiX and AuthentiX ISP - what is the difference between AuthentiX ISP and AuthentiX with a license for multiple DSN's?
First, see here.
AuthentiX ISP is for Internet Service Providers who need to support multiple customers each with their own community of users. Each customer is able to remotely administer access to their subdirectories (and only their own subdirectories)
Each customers database of usernames is separate and private from others. Customers are distinguished either by their domain's IP address, or by their host-header domain name.
If you have multiple customers, and you administer their username/passwords yourself, you could use AuthentiX with the unlimited DSN license.
However if you want them to do their own administration and it is important to you (or your customers) that each customer is unable to edit another customers usernames/passwords/configuration, then you would use AuthentiX ISP.