problem with Zanden signature DAC

I have been using the Zanden combination transport and signature 5000 DAC for a number of years,my DAC even had ann expensive trip to Japan and was updated 2 years ago.The sound is wonderful ,very musical using both the H2S and AES inputs however when I use the S/pidf input I get no sound .Any idea what may be wrong and who would be able to fix it IN the USA
I am using the same setup as yours. To my ears the sound using the H2S is easily superior to that of the other two. This is also, what Zanden suggests, if I recall right, the best way to go. So why bother at all? Just my two cents......
The reason for using the S/pidf is to try and use the Zanden DAC with the digital output of the Sooloos 10.