So how much of an upgrade is it from an HD555 to an HD650? Is it worth the extra $350-$400? Or would I be better complementing my HD555's with a good inner-ear model, like this: http://www.amazon.com/dp/B00125UBUG/?tag=neogaf0e-20 ?
Have you modded your HD555's to make them closer to the 595's? Probably worth doing before springing for the 650's.