harrogate3 wrote:

Line out is to feed to another appliance - in this case since it has
an input for Mini-Disc then it is safe to assume that the output is
intended to permit recording of whatever source is selected on the
music centre.

Indeed.

The service sheet is on http://www.eserviceinfo.com
Search for NSX-A777

MD is an line-level input for a MiniDisc.
Line-Out connects to the pins of a chip which are labelled 'rec out'.

--
Adrian C