@Grooved , are you using ASIO?
Because I see what I call the "conversion artifact bug" in all of your four plots, the one I've shown above in my plots when using ASIO.
24bit with no dither should have looked like this:
View attachment 223011
The -300dB "holes" at certain FFT bins are a good indicator whether undithered data gets handled properly.
And 24bit with dither it should look like this:
View attachment 223012
The dithering evens out the baseline noise floor as expected. Harmonics are again all below intrinsic processing noise.
I can only get this perfect pureness with WASAPI/exlusive.