Switched to M1 Mac - Why can't I export 5.1 audio for mpeg2-dvd or mpeg2-bluray files?

You export mono tracks out of premiere as quicktime multichannel audio and then setup the audio channels in compressor for dolby digital encoding.

from compressor's user manual "If you want to output a 5.1 surround sound audio file, you must first create the six channels of audio required and then import those surround sound files into
Compressor. Then you can use Compressor to output the surround sound source media file. Dolby Digital audio settings: Dolby Digital (AC-3) settings include even more audio channel
layouts, including 3.0, 3.1, 4.0, 4.1, and 5.1."

That's because AAC is not Blu-ray or DVD spec approved. Period.

For DVD you have the following 5.1 options:

1 - AC3 (support is mandatory, meaning all players must be capable of reading/outputting it)

2 - DTS & DTS 96/24 (support is optional, which means some players and/or amps may not be compatible even though it is a vastly superior codec)

For Blu-ray it gets more complex.

1 - LPCM - mandatory, all players must be capable of outputting this

2 - Dolby True HD (aka MLP Lossless with a hidden core stream in AC3)

Whilst Dolby True HD support is mandatory, the mandatory component is only stereo, which means it is very possible to have the 'True HD' lights on and only be hearing AC3. Be very careful with this. 

Also with 'True HD' you need 2 streams, the MLP & the AC3 and the 2 must be encoded by the same system, so only really the Dolby Media Producer software can provide Blu-ray legal coding. It is VERY expensive.

3 - DTS-HD Master Audio

Again, the mandatory support is stereo not 5.1 but with the DTS codec there has never been a decoder that cannot accept DTS-HD MA in 5.1 where it can accept stereo, so the odds are 99% favourable. The core stream is embedded in the Master Audio stream, so only one encoding is necessary.

Please get in touch of you need more - we do a LOT of Blu-ray & DVD.