I received my D6, and it's going straight back to iBasso for a refund.
When the unit is being used as a DAC, the maximum output of the DAC is only 1.2V peak/0.85V RMS. With a 10dB gain, this results in 2.68V RMS across the headphones, and for a 32 ohm load, this is 225mW. The specs say 650mW into 32 ohms, so the DAC is not able to get anywhere NEAR this maximum spec. In my opinion the specs are extremely misleading, because it says quite clearly that the Line Output is 1.5V RMS. If that were true, it would tally nicely with the 650mW specification, but it simply is not anywhere near the truth. The only way the Line Output can be used is when the unit is used as a USB DAC, because when the unit is being used as an analog headphone amp, that connection becomes a Line Input.
On the positive side, the unit works well for low latency ASIO, which is something I was not sure about. I was able to use an ASIO buffer size of 128 samples @44.1kHz, and I could play software pianos in real time with very low latency. I took a risk with this, and it's unfortunate that I encounterd a completely different and unexpected problem with the output drive capability!
It does sound very good (although I'm not a headphone connisseur), and iBasso are at least very responsive, and it is good that they will refund me.
Anyway, you have been warned: When used as a DAC, it will only put out 225mW into 32 ohms.
Greg.
p.s You can turn the volume up and get a >2.68V RMS level, but it will be clipped. The maximum usable sine wave output is 2.68V RMS.