The soundcard oscilloscope isn't really useful here -- we don't have a good way to calibrate it so that the measurements mean anything from one machine to another.

But you could use it yourself in isolation, to compare max volumes between the various players you may have in your possession.

Just play a standard tone (the various empeg auto-eq tracks are perfect for this) at max volume, and measure the level reported by the scope software.

I don't use Windows, nor that scope software, so I cannot be of much additional help here.

Oh, and YES, use the LINE-IN input if your soundcard has one. Otherwise the MIC input perhaps (assuming max volume doesn't fry it..).

Cheers