AAC why is downmix required

[lscolman]

Running latest version of Apollo and playing back .mp4 files.

I can get the sound with downmix on, but should I not be able to play these files with downmix off?

It's the same on my other duo2. This is on a Sony and a denon amp.

Any thoughts?

Cheers, Lee

[Joe_90]

Most AV amps don't support decoding of AAC. I have a high-end Onkyo amp which will handle all Dolby and DTS decoding over HDMI (including TruHD) from Blu-Ray players etc., plus multichannel PCM at up to 192kHz, but it won't decode AAC.