As for the cardas sound, overall, they seem to pull the image forward and upfront more. Maybe more than I wanted actually, as I now have to lower the volume a bit, compared to the stock. Some others might see this as being more "transparent" and "detailed". I don't feel that the Cardas are actually extending the highs or low any further than the 600 already is. This to me, is somewhat reminiscent of the Grado sound sound, but with a different ambience.
Upon trying on the SR325 (with comfy pad), for comparison, the soundstage is definitely alot more pronounced and upfront than with the 600/cardas, especially the mid and high.
This was done with both the zotl, melos, and supreme/cosmic. But do keep in mind that this is simply my taste and opinion. I really dislike overly extended highs and have a preference for a laid back and more relaxing soundstage ambience. This is also why I like tubes.