Regardless of how this started or how it turns out, I don't see how "some compensation for your trouble" should even enter the equation. Did the vendor harm you in some way? Let's get real.
In a fair scenario, Hifiman should ship the HE-6 back on their dime. You should get what you bought. If they're really sorry, they'll ship your HE-300 and write off the erroneous first shipment. But for them to dig further into their pockets at this point for this mistake is just plain asking too much. And that's not even considering what's taken place in this thread.
It's possible you'll get more than you asked for in this transaction and that's gotta be pretty cool, but to speak as if you're entitled to more is downright bratty. So many pages later, I don't know who said what, and I don't care. If we want to be treated fairly by merchants, the least we can do is act fairly as customers. Period.