I used the 518 as a buffer for all digital inputs into my 568 and later 568.2mm; I thought of it as a great equaliser, in as much as it made most digital sources become equal, especially with computer audio and optical from a TV; as Frank describes, "Meridianizes" any input.

You can also add gain to each source along with jitter control and resolution enhancement; very useful with TV optical outputs that always seem to be 8dB low.

The manual seems quite complicated, but it does make sense eventually.

All the best,

Steve