[PROBLEM] DSD DXD

[MikeyFresh]

i'll try with RPI4 with USB3

Curiously, the IFI spec sheet says early on: "At home or in the office, use the USB3.0 cable provided to connect to your PC." Much farther down, in the specifications it says "Input(rear): USB2.0 type A ‘OTG’ Socket (with iPurifier® technology built-in)".

amirim of AudioScienceReview stated he had to connect the IFI DAC to a USB3.0 port on his PC for it to be recognized by Windows. Others using other DACs have noted curious audio issues when they tried to drive a USB2.0 DAC from an RPI4B's USB3.0 port. So be sure to try both the USB3.0 and USB2.0 ports on the RPi4B since YMMV. 
 
Regarding DSD256 "or higher", even the IFI specs only claim DSD support "up to DSD256". Don't confuse DXD for DSD. DXD is actually a multi-bits per sample PCM encoding method. 

Also I have come across an old-ish 3rd-party review stating that the firmware upgrade which implemented MQA unfolding also reduced the max possible DSD bitrate, to wit

The only genuine negative I can come up with for this unit is that if you want both MQA Rendering support and native DSD replay capability, you have to limit yourself to DSD128 and lower. This isn’t much of a negative. There is very little native DSD content at more than 1x (DSD64), let alone above 2x (DSD128).

You might want to ask the IFI folks.

Regards,
Kent

Exactly, if using the iFi firmware that supports MQA, that would reduce the DSD sample rate support. Additionally, it also depends if DoP is employed, as DSD256 over DoP requires a PCM sample rate of 705.6kHz, also not supported by the stupid MQA firmware version if I'm not mistaken.

Unfortunately iFi now obscures this information on their support page, you have to enter a serial number to see the firmware versions available for any given product.