To the best of my knowledge, USB audio, be is UAC1 oe UAC2 support only 2 modes.
One is of course linear PCM.
The other is RAW, mostly used for DSD.
A DAC (or its receivers) simply don't understand any PC audio format. You can't send FLAC, MP3, WAV, etc. to it as it simply don't have codec's onboard. All a DAC does understand is a couple of protocols e.g. SPDIF (linear PCM packed in a 32 bit word), UAC1 or 2 (PCM or DSD), etc.
The only thing that works to the best of my knowledge is decode any PC audio format to linear PCM, pack it in a protocol and send it to a protocol converter.
That's quite a bummer, I assume that trying to send a compressed source from a computer wouldn't work, then ?
Can I ask you if you'd know by chance any hardware devices that could send a compressed audio source with an AES3, SPDIF or coax output (or anything not USB) ? I tried from an old DVD player with an SPDIF output, but the output stream seemed to be decoded by the DVD player
foobar2000 started decoding DTS out-of-the-box by version 2. In 1.x it could not decode, so it would just pass it on.
2.1 though, did something to it. From changelog:
"Added an option to toggle additional decoding (DTS, HDCD, etc) during playback, so you can play DTS-WAV without decoding DTS."
I tried also with foobar2000 1.6 too, but the issue I had here was that either it couldn't read my AC3 or DTS (because foo-input-dts wasn't installed), either it could read it with foo-input-dts, but would decode my dts stream. Do you know if an audio file can be read "raw" without having anything decoded ?
However based on Roseval answer I'm starting to doubt my whole setup : if the USB from a computer wouldn't allow to have a stream passed through to a DDC, using foobar or another software would give the same result, woudn't it ?