Schiit Magni Piety vs Schiit Vali 2+

Short answer

More power: the Schiit Vali 2+, with 1.50 W into 32 Ω; the Schiit Magni Piety has 1.00 W. Both drive 567 of the 567 non-electrostatic headphones here to 100 dB, so on that test the difference changes nothing.
Hiss with sensitive IEMs: cannot be compared — the maker of the Schiit Magni Piety publishes no noise figure.
Output impedance: 71 headphones are left alone by the Schiit Magni Piety under the one-eighth rule but coloured by the Schiit Vali 2+ (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Nio, 68 more).
Price: the Schiit Magni Piety costs $51 more; what that buys on these numbers is set out further down, under What the price difference buys.

Both are desktop amplifiers, $200 against $149.

On raw power they are level: each reaches 100 dB on 567 of the 567 non-electrostatic models here.

Every published figure, next to each other

Specification	Schiit Magni Piety	Schiit Vali 2+
Power into 32Ω	1.0 W	1.5 W
Power into 150Ω	446 mW	496 mW
Power into 300Ω	400 mW	400 mW
Power into 600Ω	200 mW	200 mW
Output impedance	0.6 Ω	1.8 Ω
Output noise	not published	25 µV unverified
Price	$200	$149
Headphones it reaches 100 dB on out of 567	567	567

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

Where each power figure comes from

Load	Schiit Magni Piety	Schiit Vali 2+
32 Ω	Published	Published
150 Ω	Derived	Derived
300 Ω	Published	Published
600 Ω	Published	Published

Both makers publish a power rating. Schiit Magni Piety publishes at 32 Ω, at 300 Ω and at 600 Ω; Schiit Vali 2+ at 32 Ω, at 300 Ω and at 600 Ω. The other rows are worked out from those.

The two publish at the same loads, which is the one case where the rows of this table can be read straight across.

What the labels mean.

The headphones that tell them apart

On power they are interchangeable across this whole database: there is no headphone here that one reaches 100 dB on and the other does not.

71 headphones are left alone by the Schiit Magni Piety under the one-eighth rule but coloured by the Schiit Vali 2+ (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Nio, 68 more).

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

Headroom and hiss on 8 models, both sources

Headroom is at a 100 dB SPL peak.

The widest gap on the list is the Shure SE846: Schiit Magni Piety has +42 dB of headroom there against +40 dB. 2 dB is about 1.6 times the power, which matters for peaks rather than for how loud the music sits.

The hiss columns are empty for Schiit Magni Piety and Schiit Vali 2+ because neither maker publishes no output noise figure.

Headphone	Impedance	Needs	Schiit Magni Piety headroom	Schiit Vali 2+ headroom	Schiit Magni Piety hiss	Schiit Vali 2+ hiss
Shure SE846	9 Ω	0.04 mW	+42 dB	+40 dB damping	not published	not published
Campfire Audio Andromeda 2020	9 Ω	4.0 mW	+22 dB	+20 dB damping	not published	not published
Audeze LCD-2 Classic	70 Ω	0.79 mW	+29 dB	+30 dB	not published	not published
Beyerdynamic DT 1990 Pro (250Ω)	250 Ω	0.63 mW	+28 dB	+28 dB	not published	not published
HiFiMAN HE400se	25 Ω	7.9 mW	+21 dB	+22 dB	not published	not published
Audio-Technica ATH-R70X	470 Ω	1.6 mW	+22 dB	+22 dB	not published	not published
Sennheiser HD 600	300 Ω	6.6 mW	+18 dB	+18 dB	not published	not published
HiFiMAN Susvara	60 Ω	50 mW	+11 dB	+12 dB	not published	not published

The gap in dollars, against the gap in numbers

The Schiit Magni Piety costs $51 more than the Schiit Vali 2+. Out of the 567 models here, that difference buys 71 more models left alone under the one-eighth rule.

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.