Not sure if this is what's causing your problem, but with my 3ft long 3.5mm to 3.5mm cable, going from my DMG to my PC's line in, I get no signal, but using a much shorter one works just fine. The output of the DMG might now be powerful enough. I also might just be talking out of my ass. lol.
edit: nevermind, I used the same cable with my amp, and it worked just fine.