You can't use the standalone gearbox within Reaper. You will need to pay for Pod Farm to use your UX2 models as a VST plugin.
The clicks and pops may be caused by dodgy drivers on your PC. Use the DPC Latency Checker (
http://www.thesycon.de/deu/latency_check.shtml) to see if there are any problems in that respect. Using this tool on my own system I found that the NIC driver and the CPU throttling was the root of my dropout problems. The latter required a visit to the BIOS to disable C1E and EIST.