1. Upgrade upsampling module before signal to PCM1732.
(we have 24bits/96KHz upsampling provide)
2. Change 4 E-cap from Elna MUSE to Blackgate. Also that 2 large 3300uF.
3. Low pass filter capacitor --> Silver Mica
4. Op-amp --> NS LME49710. (more musical than OPA627).
You can soldering a socket inside of PCB, we have OPA627BP and LME49710, you can AB comparision.
5. Resistor --> Dale or RMG depends on your budget. But sure is not using the cheap cheap default resistor.