Hi again Christian,
This is really cool, I'm glad to see this package! I see that most of your usage of the J/Link component here pertains to be able to write and read from sockets. We have the ability now (since 10.3) to connect to a socket from the Wolfram Language with SocketConnect.
For example, some of your commands could become like this:
socket = SocketConnect["ip address"];
WriteLine[socket,"DIG:PIN LED9,1"]
Then when you need to read from the socket, you can use
result = ReadLine[socket]
Ian