By not choosing a 5.1 project preset ...
When you start a project (file / new project) you can choose your project preset. You have f.e. preset 1080i WITH 5.1 sound and another one 1080i without 5.1 sound. Your original 5.1 sound will be converted to stereo in that last case.
What version of Premiere Elements are you using and on what computer operating system is it running?
From your screenshot, probably version 10 on Windows.
There are two audio track display formats = one with a black horizontal line displayed and the other the wave form displayed.
You use the speaker icon to the left of the name of the track to toggle between the two.
The 5.1 notation appears on audio tracks when your project preset description includes 5.1 channel.
So, I would ask "What project preset have you set and what are the properties (audio especially) of your source media - Stereo or 5.1 channel)?
Please give details so that I can fine tune the reply.
I did not see freeowww66 reply until after I had posted mine.
Not sure if you need more than that already mentioned, but you might want to review my blog post on Premiere Elements audio features which are
probably going to be applicable as supplemental information to your version.