Good question.

To directly answer your question, one of the reasons I bought the 2150 is because of its USB input - thinking I would get the best sound quality directly from my computer's innards. So I have been trying to make that approach work.

Isn't a computer sound card just another name for a DAC, aka digital/audio converter? I already have one - inside the Outlaw 2150. I don't understand what advantage a new "sound card", aka "DAC" would provide.

What has been people's experience with a good quality sound card compared to using the USB out to the Outlaw 2150? And how much does an upgrade quality sound card have to cost to make a noticeable difference, especially in getting rid of my existing USB digital garble?

I have to admit that 95% of the music I listen to masks the low level garble. It is primarily noticeable when there is no signal present. I guess I was expecting total quiet which I do experience when I play my Kindle Fire HDX from its headphone out jack into the 9150's front panel input - total quiet, even using a cheap cable.

Would an EXTERNAL sound card work as well as an internal? I guess it would still be subject to the same USB input noise that I am experiencing now. I don't understand how a new sound card would help. Please explain.

Will either approach (internal or external sound card) eliminate the background USB garble? Or will it become background analog sound card garble?