There is are a lot of things in play here. A few thoughts:
You can only assign one device to GPS1,2,3,4 slot at a time. Beyond that, you can use any serial port you like.
Are you seeing good sentences in the serial port menu where you're setting up the 296? If yes, then make sure you're using PFD>NAVSRC to select the 296 on SkyView. If you're not seeing the good sentences increment, see if you're even seeing the RX counter go up. If it's not incrementing, then SkyView is not getting any serial data from the 296, and you need to look at the physical connection and the 296's settings. Incidentally, you can use any of the NMEA Out / 9600 baud settings on the 296, and then make sure that in the "advanced NMEA setup" that you have data rate set to "normal", not fast.
If that didn't help, please give us a call at 425-402-0433 when you have a moment for further help.