@Mickkie - it's not an issue specific to Yamaha. Most AV amps do not process AAC. It's not that they are downmixing a 6 channel audio stream to two channels - they won't handle AAC in any format! It's the player that is downmixing the AAC 5.1 audio to PCM 2.0 because it knows that the amplifier won't process AAC. You will either have to get a player that transcodes AAC 5.1 to AC3 5.1 "on the fly" or convert the audio off-line. Or else purchase an AVR which will handle AAC natively!