Eagle CUDA 350 GPS

[dumboears]

I just got a Eagle CUDA with GPS and s Map for Christmas and I am getting it hooked up. This unit has a fully functional GPS and includes instructions for manually entering waypoint data.
It also has a NMEA 0183 port which can be used to hook the GPS up to a DSC on a VHF radio. The instructions talk about how to set this up for outputting to the radio in pretty good detail. However, it would appear from the manual that you can also set up "NMEA GPS input" The manual does not go into this in any way. It does have a section on configuring NMEA and includes turning on or off the following sentences:
GLL
GGA
APB
RMC and RMD
GSA and GSV

So my questions are the following:
Is NMEA by nature a two way conversation format? I'm not trying to do both ways at the same time but only occasionally to upload waypoint info.
Do the sentences listed above apply for uploading waypoint information?
Has anybody figured this out for this particular unit?

Thanks a bunch in advance.