This is all around awesome. Every bit of it, right down to the power strip[1] seems to be well-chosen to fit the aesthetic. Truly, a great mix of engineering and artistic skills.
Did you look at the speakers it has? Basically computer speakers from a cinema type setup.
This is very clearly a project about aesthetics and solving a problem that the individual had (integration of various audio systems - turntable + spotify), rather than one about quality of sound.
From an aesthetic perspective this is one hell of a well done job. Everything about it looks good. It won't sound incredible given the speakers used, so it is not necessary for the USB sound card and Pi to also provide a sublime and low-noise signal.
In fact one could argue that given the aesthetics, it not sounding perfect fits the design aesthetic of the project.
Sure, I have no issue with that. I just wanted to clarify that USB sound cards are sometimes very much sub-par in terms of audio quality and one should be very careful about their choice there.
If you want only to listen, USB DAC is good option.
Buy sabre based diy[1]. It's simple and uses great components - best reciver and best in its budget class dac.
1. http://audio.toddkumpf.com/power-strip#