AE4 can only convert 16-bit PCM wav files to AIFF.
Why not use Reggae for sample import in MorphOS version? With a few lines of code you have support for 20 or so formats (WAVE 8 to 32 bits, WAVE floating point, AIFF with any bit width, AIFC 'sowt', WAVE with A-law/u-law quantization, IMA ADPCM, MS ADPCM, 8SVX, 16SV and even MP3..., many of conversions are AltiVec accelerated). Anyway Zormanita can convert them all to 16-bit PCM AIFF :-).