Well I assume that AE_SINK is an enviromental variable that XBMC requires, so there are 2 approaches that I will consider:
1. Add that line to the main config file (Probably /etc/.bashrc or /etc/.profile), which distro do you use?
2. Add the same line to your user config file, ($HOME/.bashrc or $HOME/.profile)
Add the following line at the end of the file