Synergy between HD600 and Bottlehead Crack?

I don't want to refer as to which one is better but it would be bases more on you preferences. I listen to miles with a tube amp but for Metallica...I still prefer solid state. And yes...you will be smiling with hd6xx coupled with a tube amp especially with the bottle head.

The Crack was amazing with HD650s, absolutely wonderful. I'd imagine that it would be similar with the HD600s, or any other high-impedance headphones. It did NOT play nice at all with low impedance cans, however.

I don't remember if what I heard had the Speedball. IIRC, you can do the upgrade pretty easily later, so you don't need to do it right away.

I've never owned a DT880, just heard one briefly at a meet and I can't really remember what I thought of it for I was so n00bish at the time (long ago, this was). 

 

I do have the DT770, and I do prefer the HD650 by a pretty fair margin.

 

I've never found it to be muffled, but I've never attempted to listen to it not on my rig, so I can't speak about it when it's improperly amped.

 

As far as laid-back, it's not an 'in-your-face' headphone like a Grado or Ultrasone. Passive listening doesn't really do it justice, I think. I've always been one who enjoys listening actively (laying down/sitting, in the dark, doing nothing else, exploring the soundscape, searching for details), and the HD650 is extremely rewarding if you like to do that. 

I had a K701 for a while, sold it last October. DT770 is fairly bright. I've never tried an HD600, but I want to.

 

I'd say that 'in your face' is a combination of a lot of things, between attack, close soundstage, particular emphasis on any part of the freq. spectrum (not just treble). I've always thought that hot treble is sort of a way to convey illusory detail, making something sound detailed when it might not be, by emphasizing delicate parts in the music and overtones.

 

I really love my HD650s, I've had them since the beginning of my head-fi journey, and they've outlasted every other headphone that I've had other than my Pro4AATs. However, I think that any of those three that you're considering are an upgrade from your current rig. Don't discount the value of amplification and a proper source when you make that step up, though.

 

I'm sure that the built-in DAC is fine, it's a much bigger deal if you're dealing with onboard audio with computers. Obviously a nice source is always a good upgrade to make, but you'll be fine. I used the stock DAC on my CDP for about a year when I had my HD650s, was plenty happy with it.