I do use the speaker out too . If you use the alsa controls manually , it is easy to make a mistake and forget to open up both channels.
Use the scripts from Hias, and it should work.
Using speaker out means you probably also soldered some pins in the board, double check the soldering for any shorts or visible damage.
As the output stage of the D-amp uses an H bridge , you can not combine any wires from the channels.
Last resort could be to test with an image I have running here.
( or bring the te card here to test it in my setup )