Thanks for the quick response, gadgetboy! I first had to deal with issue of SSH not working with the RPi3 on-board Wifi chip (resolved by upgrading to latest version of Raspbian Jessie), and now was able to get everything up and running.
Just in case anyone else comes across this thread, the way I resolved my issue of the OSPi SD Card image just booting to an RGB Debug screen on Raspberry Pi 3 was to install Raspbian on the SD card, and then follow these instructions to download and build OSPi:
Download and Build OSPi