While I'm usually quick to grumble about rankings (rankings of any sort are an easy target, after all), I won't criticize TSN here. Up until a couple days ago, it wasn't at all certain how fully Dye had recovered from a very serious leg injury, so devaluing him in rankings made sense. It looks like Dye will be fine, but that's still not a given. If I had to rank them on the spot, knowing what we do today, I'd call it a dead heat.
That said, I agree that far too many pundits were too quick to hype Dunn as the next coming of Babe Ruth. We'll see what happens, but all those "50 hr" expectations seem too high to me. Still, he's getting hot, and if you can stand an occasional slump, he'll be a productive fantasy player.
If Burroughs is expendable, I'd drop him and grab both Dye and Dunn. If the choice comes down to only Dye or Dunn, I'd go with Dunn, considering the of you already have in place. With three studs already on your team, you can afford to take a risk. Getting both would be nice, though.