From David himself......

If there is no aux input, then it will say 'waiting'. The aux input
looks at the signal and determines when a track starts and ends and
increments the track counter.

The lines below are configurable from the player config dialog of emplode.

There are various level and signal meters on the screen, intended to
help you setup the source input and show the levels of normalisation
being applied. The bar across the bottom shows software gain, the rising
bars show DSP gain and the level meter on the right shows output level.
You'll notice that when the input level is low, the DSP gain goes high
to compensate. A good signal will have none or very little DSP gain when
playing music.