Is there anywhere to change the "volume in" level on your sound card? On mine I need to choose the source (which tends to revert to the internal CD player), and then max the "line-in" slider.

Does the amplifier have a radio tuner or CD player or other sound source? If so, do they work?

And (sorry if this seems silly but I get caught with things like this) have you chosen Phono as the source on your amplifier (if there's a choice)?

I find eventually that there's some setting I forgot to change, and once I find it, all is well.

Good luck!
JudyB