Regarding the noise increasing above 40 kHz due to the noise shaper, do the other upper midrange DACs do that, too? I just checked Amir's reviews of the E30 and 10th Mkii (both AK4493), and they simply didn't include the graph for this measurement. Neither do the reviews of the three devices mentioned in the edit.
As for performance, -135 dB 2nd and -138 dB 3rd harmonic is really top league. -145 dB 4th and -150th 5th is almost unheard of! Of the top of my head, I cannot name another DAC device this good *. Noise is also very good.
Looking at the CS43198 data sheet, it states -115 dB THD+N typ, -109 max with 24 bit data. Mediocre! With 16 bit, only -94 dB typ, 88 max. Strange!
If linearity is superb, this has to be noise. So will paralleling DACs bring down noise this much?
What's the story with 16 bit data? That's nowhere near the 98.6 dB theoretical limit, hell, you could find TDA1541A specimen that were better than this. So what is this? Nonlinearity in the 15th bit? This doesn't really make sense to me.
* edit: the DX7 with ESS (which?) beats it on 2nd (-139.5 dB) but not on 3rd (-134). 4th and 5th are signficantly worse than for the D30 Pro here.
SMSL M400 has -134 dB 2nd (slightly poorer than D30 Pro), -143 dB 3d (bestingthe D30 Pro) but completely looses out on 4th and 5th which are both around -140 dB
Topping D90 with AK4499 does not come close to M400