Used it for about a year then Upgraded to an all in one Steel Series Headphone\DAC So, I'm just parting with it because I do not use it anymore. You'll have to download the software off the Sennheiser site along with Manual.

If you want to know more about it there was a review done here: https://www.techpowerup.com/review/sennheiser-gsx-1000-audio-amplifier/

Specifications 7.1 Sennheiser Binaural Rendering Engine Recommended headphone impedance: 16-150 Ω DAC: 24-bit / 96 kHz Headphone amplifier: 1 V RMS @ 32 Ω 3.5-mm headphone output, 3.5-mm microphone input, 3.5-mm line-out Touch-sensitive controls 1.2 m rubberized Micro-USB cable 378 x 284 x 156 mm, 390 g