Portable USB headphone amps

Specs as supplied by the manufacturer.

Hegel Super $399

Digital inputs: USB micro
Outputs: mini-jack (analog) + optical mini-jack (digital)
USB interface: up to 24 bit / 96 kHz, plug & play
Noise floor: -140dB
Output impedance: Below 1 ohm
Dimensions: 1,6 cm x 4,1cm x 8,2cm / 0.6” x 1.6” x 3.2” (HxWxD)