Used to own the HA-160D, sold it when my NFB-10SE came in. I prefer the more of a ruler flat sound on Audio GD equipment vs the Burson's warmth. Plus the Burson doesn't quite drive the HE-6 to it's full potential (outputs about 1 watt into 50 ohms vs 6 watts on the NFB-10). However, the Burson can be used as a standalone amp while the NFB-10SE cannot.
The NFB-20 ($1480) and Reference 10 ($1850) can both be used as standalone amps and have a lot more power circuitry (3 r-core transformers vs 1) and better cases (weighs approximately 3x as much as the NFB-10SE). I think, but am not sure that they're also pure class A amps instead of A/B and can output 7 watts into 50 ohms.
The NFB-10SE is about $650 with the remote, TE8022 upgrade, and shipping to US. Still a great deal at this price.
Anyways Burson is releasing another headamp with more power, it should be good with the HE-6's. Lets see.