Go to Global Preferences -> SQL -> Debug and select JDBC Debug to Output Stream
Then try the connect again. After failure click on the small monitor icon on
the bottom bar.
You should see an error like:
SQLState(08004) vendor code(-908)
If it says "-908" than you have a base tcp connection issue. Either you're not
specifying the correct ports or server name, or your tunneling is not working.
If it's another error than post it here.
JDBC driver is enough. You will not need any Client SDK stuff.
The informix JDBC driver is type 4 meaning it's fully independent:
My email works... but I don't check it frequently...