The one the OP linked to is not the ODAC but a FIIO. The ODAC is a now legendary design by an anonymous experienced engineer called NWavguy (you can google him and his description of the design process, plus measurement data) who was fed up by expensive snake oil products and designed an affordable usb dac that really is about as good as the best. It is available from different sources and with different cases.See e.g. here:
https://www.jdslabs.com/products/46/standalone-odac-rev-b/ The one I bought is from Mayflower and sells for $119:
https://mayflowerelectronics.com/odac-rev-b-stand-alone/It is a basic usb DAC: you connect it to the usb port of the computer, and you connect the output to the line input of the amplifier. You normally do not need any specific drivers on the computer. Output is 2.0 Volt, just like a standard CD player. It takes its electrical power from the usb port, so no further cables are required. And it is a tiny and discreet box, smaller than a cigarette case.