main out is speakers or headphones so unless you are recording off the headphone socket you won't get a signal from aux in. Line out are the sockets on the back panel labelled 'Main Out'. The routing is shown in the diagram on page 200 of the manual.

If the sockets were correct then Line Out in the diagram should be Main Out, and Main Out should be deleted and replaced by Speakers and Headphones without the brackets.

If the Diagram were correct then the main Out sockets on the back panel should be labelled Line Out.