Short answer
Both are desktop DAC/amps, $449 against $349.
The JDS Labs Element III MK2 reaches 100 dB on 567 of the 567 models here, the WiiM Ultra on 562.
| Specification | JDS Labs Element III MK2 | WiiM Ultra |
|---|---|---|
| Power into 32Ω | 2.3 W | 150 mW |
| Power into 150Ω | 584 mW | 22 mW |
| Power into 300Ω | 292 mW | 6.0 mW |
| Power into 600Ω | 146 mW | 3.0 mW |
| Output impedance | 0.7 Ω | not published |
| Output noise | 2.51 µV | not published |
| Price | $449 | $349 |
| Headphones it reaches 100 dB on out of 567 | 567 | 562 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | JDS Labs Element III MK2 | WiiM Ultra |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Published | Derived |
| 300 Ω | Derived | Published |
| 600 Ω | Published | Derived |
Both makers publish a power rating. JDS Labs Element III MK2 publishes at 32 Ω, at 150 Ω and at 600 Ω; WiiM Ultra at 32 Ω and at 300 Ω. The other rows are worked out from those.
So the two columns are not equally firm row by row: at 150 Ω and at 600 Ω only the JDS Labs Element III MK2 figure is the maker’s own and at 300 Ω only the WiiM Ultra figure is the maker’s own. On those rows the derived number is the one to doubt first.
5 headphones reach 100 dB on the JDS Labs Element III MK2 but not on the WiiM Ultra — Moondrop PARA, Sennheiser HD 600, Symphonium Crimson, 2 more.
562 of the 567 models here reach 100 dB on both.
Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Sennheiser HD 600: JDS Labs Element III MK2 has +16 dB of headroom there against -0 dB. 17 dB is about 49 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for WiiM Ultra because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | JDS Labs Element III MK2 headroom | WiiM Ultra headroom | JDS Labs Element III MK2 hiss | WiiM Ultra hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +42 dB | +30 dB | 22 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +22 dB | +10 dB | 2 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +31 dB | +19 dB | 1 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +27 dB | +12 dB | -4 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +24 dB | +12 dB | -5 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +21 dB | +4 dB | -11 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +16 dB | -0 dB | -15 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +14 dB | +2 dB | -17 dB | not published |
The JDS Labs Element III MK2 costs $100 more than the WiiM Ultra. Out of the 567 models here, that difference buys 5 more models driven to 100 dB.
Nothing runs the other way: there is no axis here on which the cheaper of the two does better.
Only published figures count here; blank axes are counted separately.
Each in full: JDS Labs Element III MK2 and WiiM Ultra.