CUAV customer support has provided a solution that works! Hardware/firmware/software setup is the following: QGroundControl (4.3.0) for my Pixhawk2 (Cube Black) running PX4 1.14.0, GPS is the dual antenna CUAV C-RTK 2HP.
You need to follow the instructions found here: Users manual for PX4 · C-RTK系列GNSS
We had trouble finding the UPrecise software at first, but finally found a place to download it here: Unicore UPrecise application
Windows gave me a warning that the software was potentially unsafe, but it ended up being just fine.
All of the options and settings as outlined in the aforementioned instructions worked great. The only other issue was selecting the correct Serial port configuration in PX4. The C-RTK connects to the GPS2 port (not the GPS1 port). Within PX4 there isn’t an selection option for GPS2 (although some older comments say to use “202”, but that doesn’t work). I found though that GPS2 is mapped to TEL4. So for the parameter GPS_1_CONFIG, you need to select TEL4 (“104”).