Did the listening tests. Using my method not very "scientific" but I can definitely tell the difference. So for you who would think this is in my head then do so, I'm fine with your opinion.
Let's get into the sound comparison. I'm using er2se and My own headphone amplifier which has less than 0.00005% thd from 20-10khz and less than 0.0001% imd, also has more than 2.7W of output power with 16ohm load.
First of all, all these three sound much more similar than comparing to su-8. I call at least sounds correct/right to me.
All comparison is done at -16dBFS as the best measurements.
Firstly, the smsl m3, clean sounding, a tad bright, neutral sounding, as a baseline here. Not too wide soundstage, image is ok, not very upfront or very solid, but average to good. I can call great even if I only listen to m3. Will add comparison description in the next two sections.
Now dx3pro, sounds clearer, bass is a bit more solid. It just overall has a more transparent feeling, and little bit less congested. In comparison m3 has a layer of glare in the highs, I would say it feels around 8k (6-10k). A non-focused glare of brightness. And the sound stage is just a little more closed in and congested. Dx3pro is comfortably wide and deep. Very nice. The glare of m3 bothers me a bit and sometimes it is somewhat addictive.
The d30, which uses the same chip as m3, cs4398. It's actually sounds least like m3. I mean. They are still very close. But
d30 has a somewhat glassy type of sound which is similar to the glare of dx3pro but foused. Not like a layer but crafted in each texture. It's feels like at something at around 2khz and 6khz. And m3 sounds softer in texture. Kinda sounds like digital filtering problem but will investigate later. Everything is a bit more fluid than thet should. D30 overall sounds less like a cs4398 I remembered (from m3 and focusrite forte) and a bit more like pcm1794. Still sounds good tho. I some what prefer this over m3.
Now comparing dx3pro and d30, dx3pro is the clear winner. It just sounds a bit better in every aspect. It is smooth and clean and clear and sounds wide but natural way. D30 in comparison is a little warmer , thick and juicy. Kinda like a vacuum tube sound but only like 10%.
Overall, d30 is the most warm sounding one, dx3pro is in between and m3 is the most bright sounding one.
D30 is similar solid as dx3pro but dx3pro is more precise in the imaging. M3 is little soft and slightly congested.
Just for overall listening, i feel dx3pro is the best, it is more transparent sounding in every way. And d30 come close the second and m3 is the third.
They do sound very similar but I do hear consistent difference.
Possible downside of dx3pro, in comparison, it can sound lean and hollow, due to the precise imagine and transparency in all frequency range, also the natural larger soundstage. D30 has more meat to the sound.
M3 performs pretty good on its own, at -16db the total harmonic distortion (not plus noise) is a less than 0.0001% from 1khz to 6666hz. It is still less than 0.0002% at lower range. Very nice. Sound is crystal clear without any muddiness. But dx3pro is superior in terms of cleanness and transparency and soundstage.
Another thing I want to say is listening the dac is like looking through a window, you will hear the transparency and openness when it's there. Does that mean dx3pro is perfect? Idk, probably not. Because the best scenario is like open the window. But it's not far off.