Mike - all the real evidence we have says mono, especially the wiring diagram.

You have clearly been misinformed about the "balanced" input. Also, having stereo outputs from a device does not imply in any way that all inputs should be in stereo, look at any mixer for evidence.

A number of us have suggested that Yamaha use stereo jacks for everything because it is easier to mass-produce that way. The repair shop confirms this.

The "line/mic" distinction is purely about operating level; the Y2k sticks more gain into the circuit for a "mic" signal.

Thankyou and goodnight.