in aac, you can't change the sample rate because it's the bitrate who decide witch spectrum restitute.
in mp3, you can use 22 or 44 KHz, sample rate and you can see it don't make any difference because 22 KHz restitute also the spectrum until 20 KHz.
In fact, you can use 22 sample rate on mp3 until 80 kbps. So you never had a great quality with 22 KHz sample rate. It just mean that, until 80 kbps, mp3 encoder has approximativly the performance of a 22 KHz sample rate. But in reality, trebble are restitue too, because the bitrate decide of the sample rate on mp3 shoutcast encoders.
now the original poster broadcast in aac, and in aac shoutcast, you can't change sample rate. the only other way to change sample rate, is to configure soundcard to 22 or 44 khz, if you don't select "winamp" in this menu.
in this case, it's highly recommended to set your soundcard or 44 KHz, because you will enjoy all the capacities of your sound hardware.