Consider the simplicity of what’s going on here. The streamer is pulling audio data in packets off the Ethernet or WiFi, buffering them, then sending them (the same bits) out in a different protocol over the USB port. This is trivial. A simple Raspberry Pi is more than sufficient for the task. And the bits are going to be the same, no matter how expensive your streamer is.
I’ve written before about the pointlessness of using fancy external power supplies with small computers like Raspberry Pi, as well. The only situation where this could possibly make a change to the siound is if you have a very badly engineered DAC downstream of the USB port. Buy a better DAC, would be my advice – not a useless less-efficient heat-generating fancy power supply, from iFi or anyone else.