Never heard the HE300 but I want to like it more just because the HD600/580's have been around FOREVER...
Also yeah the DACport would kick the HD650's ass in that matchup haha. I honestly have no idea how they packed so much amp into something that size, included a DAC, and made it sound good...
If youre looking for something with bass body, the HD600's will leave you disappointed, I own basically an HD-600 (even has the grills), it's a neutrality beast, the treble comes off as bright to some even, it doesn't have the weight in it's tone like you seem to be looking for.
You sound like you want something very lush, silky smooth, and full bodied, I think only the HD650 really does it...
Also gotta throw in the obligatory Grado recommendation, the SR-225... the bass is pretty gnarly, yet isn't the main focus of the headphone at all