Buckshot,
Thank you for your Question.
In order to share info to a unit in the tower you would need another TZT2 unit or a TZT. The TZT9 may be a good option for the tower. What kind of boat do you have an what other equipment is installed?
Below is a link to the TZT9 referenced above.
As he said, you would need to look at the TZT9 because only the TZT one system is compatible with the NN3D. You can NOT use any TZT2 unit with the NN3D.