Humm,
I would imagine practically all Sound Cards can easily handle the Full Frequency Range of 20 to 20Khz Plus or Minus 1 Db. I have seen Test Reports on CD players that were nearly flat from 20 to 20khz.

Years ago there were carefully conducted tests to see how small a difference the human ear could detect. This was probably done using a single tone in the test. It was determined that 2 Db was about the smallest difference one could hear.

Now in a crowded bar/pub who can hear a 2 Db Difference.

There were also tests done to see how much distortion was needed before one could start to hear it. So the folks at HI FI Stereo Review Magazine ran some tests. Distortion couldn't be appreciably heard until it reached 6 percent. This was also using a single tone. Practically all modern audio gear, with the exception of many speakers easily beat those limits.

I'm not sure if anyone is making really cheap sound cards but you may know. It appears all that I have seen appear to be well engineered and constructed.

Ray E. Strode