I could add my impressions here too.. I have never had the pleasure to listen NFB12, but :
Based on all that glorious Sabre32 chip reviews, I had ordered an NFB11 (Non-USB, TCXO) unit to upgrade my Audinst HUD MX-1 dac/amp.
In orded to make this comparison as objective as posible, I compared these two units connected in a single chain (USB->Audinst->Toslink->NFB11)
The results were quite shocking for me.. Believe me or not, using HD600 headphones, the SQ difference was so small and subtle, that I had spent more than an hour finding at list one strong distinction !
Soundstage = same !
Instrument placing and separation = same !
Bass extension = same !
Bass quantity -> Audinst slightly bassyer, but not much, max 3db difference in the 70 hrz region!
Mids = same !
Highs -> NFB11 was slightly better detailed and less sibilant
Don't forget, it was a direct A to B comparison between both device, no extra AMPing or Filtering added...
At the moment I have no HQ coax cable to compare these two units separately, but I'll get in in the nearer future, as for Toslink, Audinst and NFB11 had shockingly close performance... What I am trying to say, I was always underestimating my Audinst, but after this experience, I can see why is Audinst that popular .. I think there are very few options under 300$ range worth upgrading Audinst HUD-MX1. You'll have to spend at least twice the price of Audinst HUD_MX1 , to be able hearing a clear SQ jump. May be there is actually a big winner DAC-AMP under 300$, I don't know, I thought NFB11 was the one.. May be my NFB11 has some hidden issue somewhere, but I don't think so. At least one more thing comes to my mind, there is steal not enough burn in made on my NFB11, but on Audio GD sait there is a note, that says - every single Audio GD unit is been tested for at least 100 hours (burn in) before sending.