Try Selecting Greece as the country, Piraeus as the city, Akti Kondyli as the street and 30 as the number. That should take you to the middle of a fairly short road that runs along one side of the docks. It works on my Tom Tom Via 135.
Once you have got there it shouldn't be difficult to find a suitable gate to enter and then find the correct mooring. E2 and E3 are the correct gates for Crete. If you can get so that you are driving along that road with the port on your left, gate E3 is at the north west corner. That is usually open and there is a combined ANEK/Superfast booking kiosk just inside that gate.
If that gate is closed turn left at the lights on the corner and gate E2, which I think is always open, is a short distance down that road. You will have to go up the right hand slip road to get to it. Once inside You can drive virtually the whole way round the docks so it isn't too important where you enter. If you turn left once inside it will take you back to Gate E3.
You can see the gate layout on this rather crude map, http://www.ferriesingreece.com/ferries-ports-athens.htm
The directions I gave put you about where it says E4 on this map which is an exit only gate I think and is usually closed.
Have a good journey.