Following this up a bit. I tried a SMSL PO 100 Pro with the D90 and although it had a slightly different sound using it with i2s into the D90 than the stock D90 straight from the computer with USB, it was not necessarily better. More bass, what seemed like a blacker background but less high end detail and less loud. The stock USB input was louder from my computer than going through the PO 100 Pro with USB and into the D90 with i2s. And was this difference in sound the i2s effect? Or just the PO 100 Pro with newer USB conversion?
But mostly I sent the PO 100 Pro back because it was not plug and play with the i2s input on the D90. I couldnt get the settings on either to get them to line up. At best, I did the electrical tape trick to block pin 16 mute going into the D90, put DSD pin 14 on the D90 DSD menu but I still got clicks and pops when changing songs and albums at DSD512 with the PO 100 Pro whereas the USB from my computer into the D90 just works with no pops or problems at DSD512 from Audirvana.
Yet, the PO 100 Pro experience does have me intrigued about DDCs. Especially ones with newer chips than the XMOS 208 in the D90 and newer femtoclocks than the D90 stock. Having i2s on the D90 does make it kinda future proof as opposed to USB.
But does anybody know of a DDC that made a real difference via i2s with the Topping D90 and will "just work" within the Topping D90s i2s settings, pinouts and menus plug and play? Or even a HDMI to i2s convertor that will "just work" with the D90 and take an output from my computer to the D90?