/var/run/pbx is the working directory for the PBX. If you are starting pbx manually, you can choose any directory (of course, write permissions need to be verified). On the command line you can try '/Library/pbxnsip/<the binary> --dir /var/run/<pbx wg>', where <the binary> is the pbx binary that is installed, <pbx wg> is the working directory that you can create using 'mkdir' before running the PBX.