I've been trying AmigaAmp but the sound is terrible and I have no success with AHI changes.
Your doing something wrong then.
I use AmigaAMP for playing (with mpega.library installed), and changing the settings in AHI i can get 44khz excellent quality MP3.
There are settings in AHI, i cant remember the exact name but its like channels, and you need to set a "channel" in AA, ie if AA is on "channel-2" and your changing the AHI prefs for "Channel-1" then it makes no difference. Someone here will clear that up i hope, as im not at home at the moment to check.
Kev