I am using the onboard sound card right now, I tried this with my cheap ass 90watt stereo and quality headphones....got the same results from both, I could hear all of the freqencies.....22000 was the hardest one though....and 25000 is as easy to hear as 21000....bad test? You try
http://www.ochenk.com/entry.php?id=63
http://www.ochenk.com/entry.php?id=63