After rolling with dozen of combinations, I turned back to earlier suggestion of Hiflight combination on the topkit (jazz/classical opamp (2209) and dummy buffer)...and WOW.. IMO, this is the best combination, you guys should try it... the D12 with that combination is almost as clean as 8599 without leaning on high. It is more balance but slightly less mellow compared with OPA1611/1612. I don't know why ibasso include the single dummy (short circuit pin 3,6) for D12, The buffer should be dual (short circuit between Pin 1&3 and pin 5&7) like in some post in SM3 amp forum. So I made myself 2 buffers... I think this buffer sound better and so far have not burned my D12.