For best performance at PCM you need to set "DAC Bits" to 20, so that output is dithered to 20-bit level. With TPDF dither, but you could also use something like NS9 or LNS15 noise shaper at output rates of >=352.8k.
Note that when I measure I take into account whole output spectrum up to 5 MHz or whatever needed to reach point where analog filter's response falls below constant noise floor of the DAC. If you run the DAC at 96k (NOS) there's massive amount of correlated images (distortion) in the output spectrum, so badly incomplete reconstruction. At 1.5 MHz the analog filter manages to remove practically all images and thus you are getting pretty decent reconstruction of the analog signal.
Here's -120 dBFS signal with 24-bit data:
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And here's the same signal with 20-bit NS5 noise shaped dither, at 1.4112 MHz rate:
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