Individual components of this product, namely the hardware, firmware, and host software/driver, have separate licenses. Please see the license notice in each subfolder.
In short:
Host software/driver (in subfolder "sdk"): MIT License. You are free to use this code and its binaries however you like, including in commercial software.
Hardware and firmware (in subfolders "firmware" and "hardware"): MIT License with Commons Clause. You may only use the firmware and electronics source code for non-commercial purposes. For example, manufacturing your own Helios DACs for the purpose of reselling them, is prohibited. However, if you have already purchased a Helios DAC and wish to modify the firmware for your needs, this is permitted. As is modifying or manufacturing Helios DACs for your own private use.
If you are unsure whether something is permitted, please contact Gitle at gitlem@gmail.com. In general, as long as your goal is not to use the Helios source to create a directly competing product, permission is likely to be given.