[Thermonuclear]

Those 600`s are a tad pricy when compared to 555/595, so what can they do that the others cannot ?

 

[paaj]

Deeper bass, smoother sound, better detail and actually bring joy

And it improves much better with better source and amp later.
This is my experience upgrading to HD650 from HD555. The HD555 is decent and nice all round, but the HD600/650 dances circles round it.

Don't forget the For Sale forum.

 

[71877]

Be better overal.
A more balanced presentation.
Not sounding dull, muddy or muffled.
Puncier bass.
Easy detachable dual-entry cable.

 

[Chrysoberyl]

Clarity,much better bass,much better highs.The difference is not small.

 

[tdogzthmn]

Buy one and you will see first hand. Its not a subtle difference either.

 

[DiscHead]

Everything! (with the possible exception of comfort) I find the 555s and 595s to be very comfortable, while the 600 & 650s clamp my head hard. I have read that this can be alleviated. There is no doubt the 600s and 650s are in a completely different league though.