I have the purple hearts, and ebony th-x00s (tr-x00 is removable cable), and have 6xx Massdrop and have had 660s. The Sennheisers, you will appreciate, and I find the fostex you end up loving. Although the focal elex is the best headphone I have, I still can't help but listen to the fostex when I just want to enjoy the music. You know how there are partners that are much better choices, but some that are just sexy? That's Sennheiser versus fostex. I gave the expensive 660s away because I had 6xx that I took the baffling out of, and they sounded just as good (to me) without being quite as fatiguing (sharp?). The fostex do get a wider soundstage as they burn in, and amps and DACs make a difference too. If it were me, I'd get the ebonies because they have that fostex sexiness, but are more clinical than the purple hearts or mahoganies. Purple hearts and a 6xx for not much more money than a 660, would be the best of both worlds if you can afford it. Whatever you do, you can't go wrong, because they're all excellent headphones.