AAC / m4a 520kb/s

To change the maximum bitrate for AAC (Advanced Audio Coding) in the context of an M4A file, you'll likely need to use a specific audio encoding or conversion tool that allows for custom bitrate settings. The limitation you're encountering, set at 320kb/s, may be a default setting in the software you're currently using.

One tool that allows for custom bitrate settings is FFmpeg, a powerful multimedia processing tool. If you have FFmpeg installed, you can use a command like the following to encode an AAC file with a specific bitrate:
ffmpeg -i input.wav -c:a aac -b:a 520k output.m4a

In this example:

input.wav is the input audio file.
-c:a aac specifies the use of the AAC codec.
-b:a 520k sets the audio bitrate to 520kb/s.
output.m4a is the desired output file.
Make sure to replace input.wav with the actual path to your input audio file.

Remember that not all players or devices may support AAC files with bitrates higher than 320kb/s, so it's essential to verify the compatibility with your target platform.

Keep in mind that modifying the maximum supported bitrate might not be possible in some software due to encoding limitations or standards compliance. If the tool you are currently using does not support custom bitrate settings beyond 320kb/s, you may need to explore alternative software like APKMyBoy that allows for more flexible encoding configurations.

Thanks for the reply, that's exactly what I've been doing manually for along time, but would like a GUI option... SoundConverter is awesome & very simple to use, while looking threw Soundconverter I couldn't see anything obvious to change to use ffmpeg as the encoder

Would be nice to have a box for custom encoder settings

I can confirm my device (car stereo) can play 520kb/s .. would love this option as it can't play .flac/.wav files