possible to downsample music/sound in Jet Grind Radio?

[hrb2k]

ok, i know about adx files now. i just have to convert them to wav files, downsample the wav, then convert it back to adx.

i don't know how to do it with afs files. i know that they are a bunch of adx files packed in one file and i found a tool to unpack the .afs file to reveal the adx files. i have to covert the adx like i said up above. but how do i repack the afs file? i need a tool for that, but where?