I converted the dts hd audio tracks of some mkv to pcm with this script
Code:
Get-ChildItem *.mkv -Path "E:\inputfolder"| ForEach-Object { 
    $outputFile = "$($_.DirectoryName)\$($_.BaseName)_pcm.mkv"
    .\ffmpeg -i $_.FullName -c:v copy -c:a:0 pcm_s24le -metadata:s:a:0 language=ita -metadata:s:a:0 title="ITA PCM 2.0" -c:a:1 pcm_s24le -metadata:s:a:1 language=jpn -metadata:s:a:1 title="JAP PCM 2.0" -map 0 -c:s copy $outputFile
}
But doing a check with mediainfo and also with ffmpeg some have a duration of 1ms less for both video and both audio tracks, now I don't know if this is normal or not and I understand by myself that it's a practically insignificant difference but I don't care because I want to be precise and do things in the best way, so not being an expert on such things I thought I'd ask for advice here, I've also tried extracting the tracks with gmkvextractgui, converting them with foobar2000 and reinserting them with mkvtoolnix applying 1ms delay where needed but I don't know if it's a better solution than using the script (except for the time needed of course)