UPDATE

768kHz currently is used mainly for the DoP mode, even though is actually possible making recording at this resolution.

DoP is a method for transporting DSD audio over USB that do not have a DSD native support. Each consecutive set of 16 DSD bits is stored as PCM bits in the lower 16 bits of a 176.4/24 sampling rate.

That permit to overcome the limitations of some operating system like Mac OS, which do not stream natively DSD on USB. The result is a lossless DSD playing from a PCM container. Higher the sampling, higher must be the PCM resolution for the stream. Basically a DSD256 recording should be about 705kHz into a PCM container.

Except few DACs converters capable of capturing at this resolution like RME ADI-2 FS, what I see all current recorders/audio interfaces are limited to max DXD 352.8kHZ/384kHz or DSD256, some at 192kHz PCM.

Anything beyond that is subjected to upsampling through conversion, using advanced software like HQPlayer4Pro, in combination with a high-quality DAC.

The only 768kHz recording available I know is Carmen Gomes Inc - Ray! made thanks to the RME ADI-2 FS, copied straight from the Studer A80 tape recorder.