This is a behaviour shared by many DACs. Higher rate DSD isn't always betterSo there is a trade-off between the worse Holo DAC perception of DSD512 rate and the superior behavior of 512+ modulator at this rate as compared to DSD256. Based on the measurements above is it possible to recommend for Holo DAC owners the optimal combination: DSD256 rate + ASDM7EC-Super 512+fs or DSD512 rate + ASDM7EC-Super 512+fs?
Here's the T+A DAC 200 for instance.
DSD256:

DSD512:

Noise is pushed further out, as expected, but you can see the distortion products increase, and quite significantly (upto 15dB) under 20khz.
You can still use the 512+fs modulators at DSD256. It's just that because they optimise for dynamic range rather than pushing noise further out, on some DACs (and depending on downstream components) it may not be ideal.
Jussi has mentioned that due to Holo's DSD converter acting as a moving average analog domain FIR filter, this isn't really an issue though so the 512+fs modulators work nearly without penalty at 256