Short answer
Both are audio interfaces, both at $199.
The Audient iD4 MkII reaches 100 dB on 561 of the 567 models here, the Tascam US-2x2HR on 541.
| Specification | Audient iD4 MkII | Tascam US-2x2HR |
|---|---|---|
| Power into 32Ω | 112 mW | 18 mW |
| Power into 150Ω | 75 mW | 17 mW |
| Power into 300Ω | 55 mW | 12 mW |
| Power into 600Ω | 50 mW | 7.3 mW |
| Output impedance | not published | 66 Ω |
| Output noise | not published | not published |
| Price | $199 | $199 |
| Headphones it reaches 100 dB on out of 567 | 561 | 541 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | Audient iD4 MkII | Tascam US-2x2HR |
|---|---|---|
| 32 Ω | Derived | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Derived | Derived |
| 600 Ω | Recomputed | Derived |
Only one of these two columns starts from a power rating. Tascam US-2x2HR publishes one at 32 Ω; Audient iD4 MkII publishes none at any of these four loads, so its column is worked out from power it published at other loads. Both are arithmetic on a maker’s own figures rather than guesses, and the method used for the Audient iD4 MkII understates rather than flatters — but at 32 Ω is the only load here at which its maker can be held to a figure.
20 headphones reach 100 dB on the Audient iD4 MkII but not on the Tascam US-2x2HR — Abyss AB-1266 Phi TC, Audeze LCD-5, Dan Clark Audio AEON 2 Closed, 17 more.
541 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 HiFiMAN Susvara: Audient iD4 MkII has +4 dB of headroom there against -5 dB. 10 dB is about 9 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Audient iD4 MkII and Tascam US-2x2HR because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Audient iD4 MkII headroom | Tascam US-2x2HR headroom | Audient iD4 MkII hiss | Tascam US-2x2HR hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +29 dB | +21 dB damping | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +9 dB | +1 dB damping | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +22 dB | +13 dB damping | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +20 dB | +13 dB damping | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +11 dB | +2 dB damping | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +15 dB | +7 dB damping | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +9 dB | +3 dB damping | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +4 dB | -5 dB damping | not published | not published |
These two cost the same, $199, so price settles nothing. Out of the 567 models here, the Audient iD4 MkII drives 20 models to 100 dB — 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: Audient iD4 MkII and Tascam US-2x2HR.