I started building a truepath amp from 41hz.com a while ago. I use a Monica/Mojo 3 USB-dac from diyparadise.com.
i plan using raspberry pi with volumio to feed the dac either through USB or directly with i2s.
The USB receiver converts from USB to i2s anyway with a PCM2706, but maybe it would be better to buypass so I can use over 48khz sampling rate wich is the limit for the PCM
Here is some pictures I took a while ago.