Yes, I had replaced the caps with my own file path, so that it read /home/myusername/apc/apc.so. I've tried running it with the file in both the outer server directory, and in the subdomain directory (/home/myusername/subdomain/apc/apc.so) that we're running moodle on, but it didn't work either time.
I've done some googling, but I haven't been able to find any guides that deal with shared servers and how to work around the access to the php.ini file. I thought that phprc was meant to somehow override php.ini but maybe I'm misunderstanding it.
Thanks again for all your help.