DSP Headphone Amplifier - $375

For background, I'm a professional hardware design engineer with over a decade of electronics design experience.
I've been working for a couple months on this DSP headphone amplifier using the following major audio blocks: DAC: AK4493S Amp: OPA1622 ADC: AK5572 DSP: ADAU1467 USB: PCM2706C Audio quality measurements are quite close to the DAC/ADC chip specifications, actually the chip specs are beyond the capability of the audio test equipment I currently have access to.
I have two extra units from my prototype build available, would be happy to provide at cost ($375).
The GUI design is still very much a work in progress (using LVGL & SquareLine Studio), so buyer definitely would be able provide some input to that.
Firmware updates are very easy with computer + WiFi connection to the unit.
Output Ports: * 1/4" headphone jack (32ohm to 600ohm) * toslink digital output Input Ports: * analog line input (initial prototypes use an included 3.
5mm adapter * toslink digital input * usb input (initial prototypes use an included USB adapter board) Power Management * 120VAC wall power input * On-board linear transformer * All analog power supplies are linear with extremely high PSRR Digital Signal Processor: * DSP has capability for many bands of parametric EQ, psycho-acoustic bass, mono-summing, etc.
* There is also room for many more DSP algorithms in future - current DSP utilization is less than 10%