Nice impressions pmostert!
Over the years Kingwa has built many of the nfb-10 variations and has improved them along the way. 2 years ago I asked Kingwa if he was going to build one with the sabre chipset and he said probably not. He wasn't comfortable with it for some time, hence it was all wolfson & pcm1704uk for ages.
Anyway, once he was finally comfortable with the advanced 9018 dac, he has really been able to make them shine.
So after many variations, the nfb-10 seems to have hit maturity and the 28 really is like a statement product for that line imo. Its got all the options - great case, big R-core, occ wires, 9018, totl usb & optional TCXO. Having owned the nfb10SE , the 28 is definitely a more mature dac/amp. Its also more ruthless (as you would expect a higher end dac to be). This thing is super detailed, fast as hell, neutral yet with heft & musicality. For $800, I'm pretty impressed - as I've always been with AGD.
Pmostert, make sure you keep burning it in - Audio-gd products, most notably the bigger ones, really improve with burnin. Theres a lot of parts in there that need to settle. Mine has improved so much, and still is. I've probably got 250hrs, maybe 300hrs. Also, definately give the balanced amp a go! I think AGD is even better at their amps than their DACs. Its a seriously powerful unit.