Little Dot MK II vs xDuoo MT-604

Short answer

More power: the xDuoo MT-604, with 2.00 W into 32 Ω; the Little Dot MK II has 100 mW. The xDuoo MT-604 drives 7 headphones to 100 dB that the Little Dot MK II cannot (Moondrop COSMO, Moondrop PARA, Moondrop PARA 2, 4 more).
Hiss with sensitive IEMs: cannot be compared — neither maker publishes a noise figure.
Price: the xDuoo MT-604 costs $7 less, and wherever both makers publish a figure the Little Dot MK II shows no advantage for the extra money.

Both are desktop amplifiers, $176 against $169.

The xDuoo MT-604 reaches 100 dB on 567 of the 567 models here, the Little Dot MK II on 560.

Side by side

Every published figure, next to each other

Specification	Little Dot MK II	xDuoo MT-604
Power into 32Ω	100 mW	2.0 W
Power into 150Ω	214 mW	427 mW
Power into 300Ω	300 mW	213 mW
Power into 600Ω	150 mW	107 mW
Output impedance	not published	not published
Output noise	not published	not published
Price	$176	$169
Headphones it reaches 100 dB on out of 567	560	567

Not published means the maker leaves it out, so that axis cannot be compared.

How solid these numbers are

Where each power figure comes from

Load	Little Dot MK II	xDuoo MT-604
32 Ω	Published	Published
150 Ω	Derived	Derived
300 Ω	Published	Derived
600 Ω	Derived	Derived

Both makers publish a power rating. Little Dot MK II publishes at 32 Ω and at 300 Ω; xDuoo MT-604 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 Little Dot MK II figure is the maker’s own. On those rows the derived number is the one to doubt first.

What the labels mean.

What separates them

The headphones that tell them apart

7 headphones reach 100 dB on the xDuoo MT-604 but not on the Little Dot MK II — Moondrop COSMO, Moondrop PARA, Moondrop PARA 2, 4 more.

560 of the 567 models here reach 100 dB on both.

On real headphones

Headroom and hiss on 8 models, both sources

Headroom is at a 100 dB SPL peak.

The widest gap on the list is the HiFiMAN HE400se: xDuoo MT-604 has +23 dB of headroom there against +10 dB. 13 dB is about 20 times the power, which matters for peaks rather than for how loud the music sits.

The hiss columns are empty for Little Dot MK II and xDuoo MT-604 because neither maker publishes no output noise figure.

Headphone	Impedance	Needs	Little Dot MK II headroom	xDuoo MT-604 headroom	Little Dot MK II hiss	xDuoo MT-604 hiss
Shure SE846	9 Ω	0.04 mW	+28 dB	+42 dB	not published	not published
Campfire Audio Andromeda 2020	9 Ω	4.0 mW	+8 dB	+22 dB	not published	not published
Audeze LCD-2 Classic	70 Ω	0.79 mW	+22 dB	+31 dB	not published	not published
Beyerdynamic DT 1990 Pro (250Ω)	250 Ω	0.63 mW	+26 dB	+26 dB	not published	not published
HiFiMAN HE400se	25 Ω	7.9 mW	+10 dB	+23 dB	not published	not published
Audio-Technica ATH-R70X	470 Ω	1.6 mW	+21 dB	+19 dB	not published	not published
Sennheiser HD 600	300 Ω	6.6 mW	+17 dB	+15 dB	not published	not published
HiFiMAN Susvara	60 Ω	50 mW	+4 dB	+13 dB	not published	not published

What the price difference buys

The gap in dollars, against the gap in numbers

The Little Dot MK II costs $7 more than the xDuoo MT-604, and on these three axes the money buys nothing: among the 567 models here there is not one that the Little Dot MK II handles and the xDuoo MT-604 does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper xDuoo MT-604 drives 7 models to 100 dB that the Little Dot MK II does not.

Only published figures count here; blank axes are counted separately.

Each in full: Little Dot MK II and xDuoo MT-604.