Headphone Splitter, Syncwire Nylon-Braided [0.75FT/23CM] Stereo Audio Y Jack Splitter Cable - 3.5mm Male to 2 X 3.5mm Female Adapter for Apple, Samsung, Smartphones, Media Players & More - Black

AudioQuest - DragonFly Red USB DAC/Headphone Amplifier

EarStudio ES100 - 24bit Portable High-Resolution Bluetooth Receiver/Headphone Amp/DAC with AAC, aptX, aptX HD (BLACK)

BoomCloud 360 BoomStick In-Line Wired Headphone Audio Enchancer Amp and Signal Processor - Black

FiiO A3 Portable Headphone Amplifier (Black)

Neoteck Headphone Amplifier Portable 3.5mm Audio Rechargeble HiFi Earphone Headphone Amplifier with Lithium Battery and Aluminum Matte Surface Ideal for MP3 MP4 Phones Digital Players and Computers

FiiO E10K USB DAC and Headphone Amplifier (Titanium)

Nano iDSD Black Label Portable DAC and Heaphone Amplifier by iFi audio

CHORD Electronics Mojo, ultimate DAC/Headphone Amplifier, USB, Coaxial, and Optical, Black

Pyle-Pro PHA40 4-Channel Stereo Headphone Amplifier