I use Siren Jukebox from Sonic Foundry to convert my CD collection (in 160bit WMA) to 128bit MP3 when I load songs onto my (Diamond Rio 500) MP3 player. I run it on my Win98 box.
Similarly, it will do bitrate conversion of MP3s - but make sure there is enough information in the original signal to do a proper conversion!
As I mentioned in another thread, 22Khz sampling gives you only an 11Khz audible range - you really need at least 20 for good sound (this is why at least 44Khz is the standard for audio hardware).
Zonyl, let us know how things go with NetBSD...