Well I have now managed to create a Pi that works direct out from the USB (in the past never managed using Picoreplayer probably my lack of technical skill) . Have then tried and completed using Max2play both a Pi 3 + and an RPi 4 2TB .

In both cases this has been just in to a simple USB to SPDIF converter but I did borrow an MDAC over the weekend and it worked just as easily in to that . Both work well and sound pretty much the same so much so that I feel it would be very difficult to identify one over the other. However I will stick my neck out and say that the RPi 4 seems to be more stable and has a lower noise floor than the RPi 3 which given that the RPi 4 has a full USB 3.0 set up is to be expected.

In my view the sound quality is excellent and given the really cheap nature of this set up it will take quite a large investment in over specified and perhaps wasted hardware to get the same result . All the RPi is doing is transferring the stream to the DAC of your choice and this will have the biggest influence on the final sound quality .

This is now not only possible but if you have a USB DAC would be my recommended scheme for adding streaming music both live and from your Library to your system .