Will Roon do 512 DSD with RPi 4 running DietPi?
You haven’t provided enough info to answer this.
DSD512 requires “native USB DSD” support. On Linux-based systems, that requires the USB DAC be “known”. sound/usb/quirks.c has all the detection logic. If you are using a DAC that uses XMOS, Theysecon or a couple other chipsets, AND it uses the respective VendorID instead of a “vanity” VendorID, then there is a good chance it will be regonized and “just work”. Otherwise it will only work if you get the DAC vendor to submit a patch for quirks.c to mainline and then that trickles down to the various RPI “audio endpoint” distros such as RoPieee and DietPi.
tl;dr: It depends on what DAC you are using.
I’m using a Pro-Ject Digital S2.
Then yes, you should be fine. This has been supported in the Linux kernel for some time now. I can personally confirm that RoPieee’s kernel recognizes it properly. I’ve never tried DietPI, but I would expect it to as well.
I’ve used both 3&4 models for dsd512 supported usb dacs but only on lan wired, but this was with ropieee