Found the similar post in R33, so assume is same person la,
As mention in R33, the headphone output is OK, therefore:
1. DAC is OK
2. I/V conversion stage is OK, if needed. (op-amp base tpically)
3. LPF stage should be OK. (op-amp base typically)
4. Headphone amp OK (op-amp base)
5. Line buffer stage (Check this la)