Short answer
Both are dongles, $179 against $190.
The Moondrop Moonriver 2 Ti reaches 100 dB on 565 of the 567 models here, the Astell&Kern HC3 on 561.
| Specification | Astell&Kern HC3 | Moondrop Moonriver 2 Ti |
|---|---|---|
| Power into 32Ω | 125 mW | 280 mW |
| Power into 150Ω | 27 mW | 79 mW |
| Power into 300Ω | 13 mW | 53 mW |
| Power into 600Ω | 6.7 mW | 26 mW |
| Output impedance | 2.0 Ω | not published |
| Output noise | not published | 1.5 µV |
| Price | $179 | $190 |
| Headphones it reaches 100 dB on out of 567 | 561 | 565 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | Astell&Kern HC3 | Moondrop Moonriver 2 Ti |
|---|---|---|
| 32 Ω | Upper bound | Published |
| 150 Ω | Upper bound | Derived |
| 300 Ω | Upper bound | Published |
| 600 Ω | Upper bound | Derived |
These two columns are not the same kind of number, and that matters more than the gap between them. Moondrop Moonriver 2 Ti publishes a power rating (at 32 Ω and at 300 Ω); Astell&Kern HC3 publishes no power figure at any load, only a maximum output voltage, so every milliwatt in its column is a ceiling worked out from that voltage.
A ceiling assumes the amplifier holds that voltage into the load, and nothing on Astell&Kern HC3’s own sheet says it does. It is the most flattering reading available, and it is used here only because the alternative is a blank. Where the Astell&Kern HC3 column looks the stronger of the two, treat the difference as unproven rather than measured. 24 of the 280 sources here are in that position, with no published power rating at any load.
4 headphones reach 100 dB on the Moondrop Moonriver 2 Ti but not on the Astell&Kern HC3 — Moondrop COSMO, Symphonium Crimson, Symphonium Helios, 1 more.
561 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: Moondrop Moonriver 2 Ti has +9 dB of headroom there against +3 dB. 6 dB is about 4 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Astell&Kern HC3 because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | Astell&Kern HC3 headroom | Moondrop Moonriver 2 Ti headroom | Astell&Kern HC3 hiss | Moondrop Moonriver 2 Ti hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +29 dB damping | +33 dB | not published | 18 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +9 dB damping | +13 dB | not published | -2 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +19 dB | +22 dB | not published | -4 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +14 dB | +20 dB | not published | -8 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +11 dB | +14 dB | not published | -9 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +7 dB | +13 dB | not published | -15 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +3 dB | +9 dB | not published | -19 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | +1 dB | +5 dB | not published | -21 dB |
The Moondrop Moonriver 2 Ti costs $11 more than the Astell&Kern HC3. Out of the 567 models here, that difference buys 4 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: Astell&Kern HC3 and Moondrop Moonriver 2 Ti.