Bon, j'ai trouve ds la FAQ du forum Audio de doom9 :
AC3->MP3. which AC3 stream should i decode ? 5.1 or 2.0 ?
the 2.0 stream has a better mix for 2 channels (stereo), than the 5.1 to 2.0 downmix features offered by AC3 decoding tools. therefore, it should be the best to work with the 2.0 stream.
there is only one case when transcoding the 5.1 stream is better :
if your computer has connection to a dolby pro-logic decoder, you could use a surround downmix, and then your dolby pro-logic decoder would reconstruct the multichannel audio.
Donc le 2Ch serait meilleur. Qu'en dites-vous ?