Connection Question

I have a NAD C328 integrated that has 2 digital and 2 optical inputs . I don't know anything about details .

Your NAD C328 amp has 4 digital audio inputs (2 optical/2 coaxial). It does not have a USB input connection. If your Chromebook only supports USB output, you are going to need a digital to digital convertor was suggested above.

For example:

DOUK Audio Converter

I think the above will work but please confirm this.  Search on USB to optical converter for additional options.   

I 'm going to try to get more info on this converter . It's on Amazon for $ 56 . Thanks for the link .