Short answer
Both are audio interfaces, both at $199.
The Focusrite Scarlett 2i2 4th gen reaches 100 dB on 552 of the 567 models here, the Tascam US-2x2HR on 541.
| Specification | Focusrite Scarlett 2i2 4th gen | Tascam US-2x2HR |
|---|---|---|
| Power into 32Ω | 31 mW | 18 mW |
| Power into 150Ω | 19 mW | 17 mW |
| Power into 300Ω | 22 mW | 12 mW |
| Power into 600Ω | 11 mW | 7.3 mW |
| Output impedance | 50 Ω | 66 Ω |
| Output noise | not published | not published |
| Price | $199 | $199 |
| Headphones it reaches 100 dB on out of 567 | 552 | 541 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | Focusrite Scarlett 2i2 4th gen | Tascam US-2x2HR |
|---|---|---|
| 32 Ω | Derived | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Derived |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. Focusrite Scarlett 2i2 4th gen publishes at 300 Ω; Tascam US-2x2HR at 32 Ω. The other rows are worked out from those.
So the two columns are not equally firm row by row: at 300 Ω only the Focusrite Scarlett 2i2 4th gen figure is the maker’s own and at 32 Ω only the Tascam US-2x2HR figure is the maker’s own. On those rows the derived number is the one to doubt first.
11 headphones reach 100 dB on the Focusrite Scarlett 2i2 4th gen but not on the Tascam US-2x2HR — Abyss AB-1266 Phi TC, Audeze LCD-5, Dan Clark Audio AEON 2 Closed, 8 more.
3 headphones are left alone by the Focusrite Scarlett 2i2 4th gen under the one-eighth rule but coloured by the Tascam US-2x2HR (Audio-Technica ATH-ADX5000, Audio-Technica ATH-R70X, Audio-Technica ATH-R70xa).
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 Sennheiser HD 600: Focusrite Scarlett 2i2 4th gen has +5 dB of headroom there against +3 dB. 3 dB is about 1.8 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Focusrite Scarlett 2i2 4th gen and Tascam US-2x2HR because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Focusrite Scarlett 2i2 4th gen headroom | Tascam US-2x2HR headroom | Focusrite Scarlett 2i2 4th gen hiss | Tascam US-2x2HR hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +23 dB damping | +21 dB damping | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +3 dB damping | +1 dB damping | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +14 dB damping | +13 dB damping | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +15 dB damping | +13 dB damping | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +5 dB damping | +2 dB damping | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +9 dB | +7 dB damping | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +5 dB damping | +3 dB damping | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | -3 dB damping | -5 dB damping | not published | not published |
These two cost the same, $199, so price settles nothing. Out of the 567 models here, the Focusrite Scarlett 2i2 4th gen drives 11 models to 100 dB and leaves 3 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: Focusrite Scarlett 2i2 4th gen and Tascam US-2x2HR.