All I'm saying is that you don't HAVE to use their drivers. If you have them and they work, great. If not there are a lot of options available to you. If you do use their drivers test them carefully as some drivers I got from them a few years ago were very buggy.
There is also no need for playing with OPC, DataSockets or any of the rest. All you need is a serial port and a set of drivers that know how to talk Modbus--which by the way isn't a very complicated protocol. In fact, I once wrote a set of drivers myself just for the practice.
Mike...