Short answer
Both are desktop amplifiers, both at $99.
The Schiit Magni Heresy reaches 100 dB on 567 of the 567 models here, the JDS Labs Atom+ (2nd gen) on 566.
| Specification | JDS Labs Atom+ (2nd gen) | Schiit Magni Heresy |
|---|---|---|
| Power into 32Ω | 1.0 W | 2.4 W |
| Power into 150Ω | 545 mW | 641 mW |
| Power into 300Ω | 272 mW | 410 mW |
| Power into 600Ω | 136 mW | 215 mW |
| Output impedance | 0.7 Ω | 0.25 Ω |
| Output noise | 1.99 µV | 1.5 µV unverified |
| Price | $99 | $99 |
| Headphones it reaches 100 dB on out of 567 | 566 | 567 |
| Load | JDS Labs Atom+ (2nd gen) | Schiit Magni Heresy |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Published | Derived |
| 300 Ω | Derived | Published |
| 600 Ω | Published | Published |
Both makers publish a power rating. JDS Labs Atom+ (2nd gen) publishes at 32 Ω, at 150 Ω and at 600 Ω; Schiit Magni Heresy at 32 Ω, at 300 Ω and at 600 Ω. The other rows are worked out from those.
So the two columns are not equally firm row by row: at 150 Ω only the JDS Labs Atom+ (2nd gen) figure is the maker’s own and at 300 Ω only the Schiit Magni Heresy figure is the maker’s own. On those rows the derived number is the one to doubt first.
1 headphone reaches 100 dB on the Schiit Magni Heresy but not on the JDS Labs Atom+ (2nd gen) — Symphonium Titan.
4 headphones are left alone by the Schiit Magni Heresy under the one-eighth rule but coloured by the JDS Labs Atom+ (2nd gen) (Campfire Audio Chimera, Moondrop Armature Art 12, Softears Volume, 1 more).
566 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 Campfire Audio Andromeda 2020: Schiit Magni Heresy has +26 dB of headroom there against +18 dB. 7 dB is about 5.6 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Schiit Magni Heresy because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | JDS Labs Atom+ (2nd gen) headroom | Schiit Magni Heresy headroom | JDS Labs Atom+ (2nd gen) hiss | Schiit Magni Heresy hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +38 dB | +46 dB | 20 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +18 dB | +26 dB | 0 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +29 dB | +32 dB | -1 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +27 dB | +29 dB | -6 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +20 dB | +25 dB | -7 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +20 dB | +22 dB | -13 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +16 dB | +18 dB | -17 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +11 dB | +14 dB | -19 dB | not published |
These two cost the same, $99, so price settles nothing. Out of the 567 models here, the Schiit Magni Heresy drives one model to 100 dB and leaves 4 alone under the one-eighth rule — and on the other side there is no such advantage at all.
Only published figures count here; blank axes are counted separately.
Each in full: JDS Labs Atom+ (2nd gen) and Schiit Magni Heresy.