I have a lot of respect for Paul Miller and the work he does for Hi-fi News and their sister company Stereophile.
However, this is a pretty lazy take on the DSD1793 chip capabilities as installed in the iFi Diablo v2, and any iFi product that uses the 1793, for that matter. Paul is usually much better than this.
NO, the iFi DSD1793 engine is NOT limited to merely DSD64 and PCM 192. Perhaps in yesteryear; however in modern implementations the chip natively decodes DXD x2 and DSD1024.
The limitations exist only in the chip logic and clock. The easiest way to demonstrate this is with 1 bit DSD. The DSD1793 converter is a 1-bit FIR filter. To convert DSD 128, DSD 256, etc, all that is required is a doubling of speed into the converter/filter. The resistors (switches) in the filter know no difference. And later in the data sheet, you will find the DSD1793 bit clock timing runs as fast as 50mhz, which is just enough for DSD1024.
Thorsten Loesch, the designer of the iFi DSD1793 chipset/FPGA, has the following to say:
"Paul read the front page of the datasheet and didn't test.
Can't blame him. It's ultimately a failing by iFi's marketing people.
If you operate something outside standard parameters (which doesn't mean it risks damage or problems) you need to make sure to let people know.
The iDSD diablo 2 uses DSD1793 DAC chips. According to the front page of the datasheet, the Chip is listed as 192kHz and DSD64.
Looking inside the datasheet you can see that there is a "digital filter bypass" Operation mode that allows 768kHz PCM to be input into the chip.
Additionally, while only specified for DSD64, if you look at the DSD bit clock timing specification, it lists 20nS minimum Cycle, which is 50MHz.
Thus the DSD1793 is actually, according to the datasheet and if implemented correctly capable of 32kHz - 768kHz PCM and DSD up to 50MHz or DSD1024."
Bottom line... we love you here at Euphonic Review Paul. Your work stands alone above the rest for many decades. However, here a correction is required.