Q: Airport express not able to stream music

I am trying to use airport express on existing wireless to stream music to my stereo system.  I connected the line out cables from the AExpress to the stereo system (have not connected the AExpress to the modem).  However the amber light is flashing.  I checked the wireless is working and am not sure if I have to install anything else - perhaps the Airport Utility?  I installed the CD that came with the AExpress on my imac (from where I am going to stream the music).

Anyone any ideas?

Thanks