@Thorsten Loesch
Before buying this iFi I was using Musical Fidelity's M1SDAC.
It has almost the same chip as the iFi, DSD1796 a little newer.
I don't know why Musical Fidelity didn't enable DSD on it, only 192Khz.
As the vast majority of my files are DSD I ended up buying the iFi, even though I still have the Oppo 205 that plays DSD.
In summary, listening to the DSD files had no difference in quality for me.
I might have an idea why.
The various TI PCM/DSD labelled DAC's that can process both DSD and PCM dramatically reconfigure the way they work internally and this takes a little time and needs explicit software intervention via I2C control of the DAC IC, PLUS analogue domain muting, lest the DAC goes Rickey Martin (she bangs).
Unlike for example ESS DAC Chip's that accept DSD and PCM on the same pins and handle this transparently.
So first you need to place the DAC Chip into software controlled mode and correctly configure it, you need to get sequencing of the process right between USB interface and DAC Chip by outputting enough zeros for PCM to clear the buffers and DAC registers down to zero or by sending DSD silence instead if playing DSD.
Then the Analogue output must mute, the DAC chip's output stage must be turned off (this is not mentioned in the datasheet BTW), the chip must receive the command to switch between DSD/PCM and then the Chip output must be re-enabled and and the analogue side unmuted.
This requires typically programming on the USB Input Chip side if it is XMOS, as XMOS's reference code does not do this "send XX clock cycles of zero" and secondly, as the USB chip kinda works on it's own timing with the PC, it must be made sure that the whole changes on the DAC side are completed by the time the USB Chip starts the new stream or the beginning of the song is cut off.
This means using an interrupt-driven system on the MCU. As usually the person programming the MCU knows nothing of what happens on the USB Bridge side and visa versa and both tend be ignorant of how the DAC Chip actually works, this is not the easiest thing to achieve.
This is one of the reasons why few manufacturers use BB/TI Chip's of "advanced segment dac" type with high sample rates and DSD (even though it can be done) and instead prefer a Chip like ESS where non of this has to be done. Not everyone wants to get their product "just so".
Many Chinese outfits just want to copy/pasta from datasheets, do no extra programming work and then shift boxes to make money, what the result sounds like is of no consequence to them. This is much easier if using ESS (ideally one with 2V line out), just use XMOS reference code with ID's and Vendor name adjusted (or not even that) and an ESS Chip, voila, you have a "world leading DAC". It will even measure better than something using BB/TI in most cases. perfect for box shifters and objectivists.
Thor