OK. Thanks for your hints. I will probably buy a new player.
But by testing there was a new question.
I did the following:
ffmpeg -i "quelle.dsf" -ar 96000 -af lowpass=f=30000 -c:a pcm_s24le -filter:a "volume=4dB" -map_metadata -1 "ffmpegout96k.wav
and:
sox -V3 -S "quelle.dsf" -b 24 "soxout96k.wav" rate -v 96000 gain +4 sinc -30k
The result was two identical files.
FFPROBE:
Stream #0:0: Audio: pcm_s24le ([1][0][0][0] / 0x0001), 96000 Hz, 5.1, s32 (24 bit), 13824 kb/s
However, after converting to .flac files, I have different bitrates.
Input #0, flac, from 'ffmpegout96k.flac':
Duration: 00:17:07.24, start: 0.000000, bitrate: 8366 kb/s
Stream #0:0: Audio: flac, 96000 Hz, 5.1, s32 (24 bit)
Input #0, flac, from 'soxout96k.flac':
Duration: 00:17:07.24, start: 0.000000, bitrate: 6655 kb/s
Stream #0:0: Audio: flac, 96000 Hz, 5.1, s32 (24 bit)
I can't explain why?