I have never heard anything from Stax which is why I was checking about the Denons. I considered purchasing these this morning given their price point but AliExpress isn't getting the best of reviews, especially with suppliers not sending products and people not being able to get refunds. I might wait till they're available from a more reliable source.
I just looked up the BossHifi. Damn those look stunning. Even thicker earpads than the Denons. Your sound impressions are relative to the Denon or is it just the looks they have in common? If these are the real deal, then they're a bargain!
I auditioned the Nighthawk for about 15 minutes a few months ago. Paired with my Fiio X3II, their sound strongly resembled that of the Denon. I couldn't do an A/B comparison though as I had my Marshall Monitors on me at the time. I actually liked them but couldn't justify the price difference. Maybe I needed a more upmarket DAC/DAP to fully appreciate their full potential.
I pair my Denon with the Fiio X3II and the treble is spot on, even without any equaliser. If I use it with any of the smartphones we have at home, being a Sony Xperia Z2 or Huawei Mate 7, then it's a little too bright for my liking. So getting the right source is key. What are you using?