The sound was somewhat better with the earbuds when I put the CD into my Onkyo C-7030 and used the headphone jack. Everything changes when I use coax from the Onkyo to the SMSL SU-8, then balanced connectors from there to my Matrix HPA-3B, and a balanced cable to my Sennheiser HD800S headphones.
https://www.amazon.com/Decoder-SMSL-2ES9038Q2M-768kHz-Balance/dp/B07DQDNF6S

