Creative Sound Blaster E1 Portable Headphone Amplifier with Integrated Mic and Dual Headphone Jacks for PC and Smartphones | Headphone Reviews and Discussion - Head-Fi.org
TeachLogic Maxim III Classroom System with 4 In-Ceiling Speakers and Microphone
Alpha Design Labs ADL X1 portable DAC + headphone amp review | The Headphone List
MAX9723 Datasheet and Product Info | Analog Devices