I love Addressix but it uses a non-standard print dialogue and can get "confused" if you switch between multiple printers. Here's how to fix this problem:

1 - Download and install the free app Pref Setter 2.0.

2 - Navigate to [user] -> Library -> Preferences -> a-sharp.addressix.plist.

3 - Control-Click (or Right-Click) a-sharp.addressix.plist, go down to Open With and select Pref Setter.

4 - In the main Pref Setter window, scroll down to printerName and double-click the name in the Value column.

5 - Change the name of the printer to the desired printer.

6 - Go to the File menu and Save the new setting.

7 - Quit Pref Setter and you're good to go.

8 - Send a donation to the author of Pref Setter.

Perhaps this tip will help someone else with the same problem I had.