The 204 is about 1/3 of the cost of a 501 for one thing. Lower end chip? lol. The 9018S is a $35usd chip when purchased in quantities. The 9038Pro is $63usd and the specs are only marginally better if they are even audible. I have a 204 and it blows my U18 DDC+X26Pro(both with sr purples) and OCXO into the weeds. That's a great sounding setup but just it can't match the 204.
I don't give a crap about measurements. All I know is my 204 still in the burn in process (and still with the cheapo SMPS) has micro detail, bass, and overall soundstage and dynamics that can't be matched by the X26Pro with it's 2 9038Pro chips, a DDC and master clock.
Another reviewer who spent significant time with the 501 indicated the 204 has the same Weiss sound as if it's coming off a master tape as the 501/502. Which also, BTW, don't have 9038Pro chips either. I don't see anyone bemoaning the fact those $10k+ DAC's don't have 9038Pro chips.
I listen with my ears not scopes or measurements and the 204 is a keeper to my ears. Weiss does better with a 'lesser' chip than others with a more costlier chip(s). There's a reason Daniel Weiss won a grammy for his design work. Luckily I got mine at the original price but unfortunately with the 204 price increase last month I can see where it is now less desirable to some especially if they fret over not having a 9038pro chip.