The distinction between Magna's and Bucky Lee's comments is simply this:
Although the NT4 does not have bulit-in support for multiple video cards, you can still pull it off if you have third-party software to manage the video cards and multi-monitor functionality. Hydravision, the software that comes with Appian products, can manage up to four Appian cards at once, so in your case you could add another Jeronimo Pro to your system with no problem. However, you might have a hard time finding another two-port Jeronimo Pro, as they have been discontinued for quite a while.