iFi Audio Zen Can 3

Bass Boost, gain switch

FiiO KA11

USB-DAC

FiiO LT-TC5

Hifiman Serenade

USB-DAC, Bluetooth

Hifiman GA-10 headphone amplifier

gain switch

Hifiman EF500

gain switch

Hifiman Serenade WiFi headphone amplifier

USB-DAC, Wi-Fi

Hifiman EF400

Tone control

Hifiman Mini Shangri La J electrostatic headphone system

Microphones, USB-DAC, gain switch

Mackie Hm-800

gain switch

FiiO K11 R2R

Display, gain switch, USB-DAC

Terratec HA-1 batch

Bass Boost, Powerbank

InLine Replacement Tube for AmpUSB HiFi DSD Headphone Tube Amplifier

Mackie Hm-400

FiiO BTR13

Microphones, USB-DAC, Tone control, Display, Bluetooth