I just now unsuccessfully tried to install the Silver Efex Pro 2 plug-in to LR CC. So, I reviewed the website and, much to my surprise, it indicates that the plug-in does not support Windows 10, LR 6 or LR CC. (The website also indicates that Photoshop CC 2015 is not supported, but that's not my immediate concern.) I assume they're not supported because none of those products are listed among the programs that are supported.
I had no issues installing the plug-in to Lightroom 5 with Windows 7. If you have successfully installed Silver Efex Pro 2 as a plug-in to Lightroom CC using Windows 10, please let me know perhaps what I should try.
Thanks in advance!