While they do both share a DAC chip, the circuitry surrounding them is very different so they won't necessarily sound the same. According to the specs, at 300 ohms, the HD650's nominal input impedance, the Aune puts out 200mw while the NFB-11 manages 300mw. The HD650s need 60mw to get pretty loud, so both amps are fine for power. Audio-GD has built a strong reputation over the years and the NFB-11 is probably their most popular device now that the NFB-15 has been discontinued. Honestly, I don't think there is much between them, the Aune looks a lot nicer but the Audio-GD, while lacking in the looks has tried and tested internals.
At $305 + $37 + import duty, which is anyone's guess, the Audio-GD will be the more expensive of the two, although I don't know where you are sourcing the Aune as it's not available on the rain forest.
I did toy with the idea of getting an NFB-11 at one point but was put off by the strange purchasing method of emailing for a quote, followed by paying by Paypal and getting stung for $37 for delivery and god knows how much at customs. Then there is the issue of what to do if something goes wrong - it would have to be shipped back to China and then you'd likely get stung again for import duty when it returned to the UK.
I took the easy way out and went the Schiit route instead.
For that kind of money you could also get a very impressive Schiit stack...
Schiit Modi Multibit (£270) + Schiit Vali 2 (£165) or Schiit Magni 2/Uber (£110/£150) if you prefer solid state.
The Multibit DAC is not as analytical as the SABRE ES9018 in the two Chinese units but is far more musical if that is your preference, while all of the amps can drive HD650s with ease. One big benefit being, you can buy them in the UK and get a UK warranty.
