I believe the cx is USB only (but check to be sure). If so, it will not work with the 996. The 996 will only work with GPS that have standard serial output. There is a list of known compatible models on the 996 wiki page. You will need the GPS serial cable specific to your GPS model (it is the same one you would purchase or need to connect the GPS to your PC's serial port).
Not the C or CX plain jane vista (no color). I have had this gps for about 6 years. Used mostly for hiking and hunting.
I found that the windshield suction cup mount bracket works the best for my truck. The "movable" mount for the dash really does not work good as the base pads do not like to be moved.
You can also get a combo serial / cig adapter power cord but the unit come with a serial cable,
According to the O/M, the RoadMate 300R unit only supports USB connection to a PC. It does not offer NMEA serial output, so it will not work for this application.