NX/SSH remote access with Remmina
Solution 1:
Remmina actually has a separate plugin for connecting to NX servers. You can get it by installing the remmina-plugin-nx package. Once you install that, you will have NX available in the Remmina connection dialog.
You may also want to try a separate program called qtnx. It's also available in the Software Center. It's a little simpler and seems to work better for me when connecting to NX servers.