Hi and welcome to the Forum!!!
I presume that you have wired it to your stereo.
If so, does your stereo have a headphone Socket???
If it does then that is the one you need to use.
If not, your Pandora may be by-passing the headphone socket but still eliminating the built in Speaker Units as per normal.
Double check the wiring that you have done and if it is all wired up correctly then I suggest that you give the help line a call to see what can be done, other wise you will have to make some modifications to the unit itself which will nullify the Warranty.
Is it as good as they say it is???
Get a Newbie post up too as soon as you can
El