You asked an extremely vague question and got a very broad answer. None of the headphones I listed are overly sibilant or harsh sounding, and none of them cost more than $600 (the AH-D5000 probably do today though). Do you have a problem with that? You had no other criteria.
And yes, the Beats *are* horrible. But they're under $600 and aren't sharp, piercing, or harsh. Fits your criteria.
(No, I would not suggest them, hence why they didn't get listed).
As far as the Bose headphones - they have fine sound quality if you're looking for a laid-back and non-fatiguing sound, they just aren't extremely dry or bright, which separates them from a lot of "audiophile" products. Depending on what you actually want here, the AE2 might not be a terrible choice.
I'll finally add, since I think it would probably be helpful for you to hear this sooner rather than later - there is not going to be a singular "best" choice, there's going to be a best choice for you, based on a variety of factors, so expecting to be spoon-fed is probably not going to get you a product you really want to have. But who knows, you might get lucky.
And as I said - provide more criteria and I'll refine the list for you (I do mean it).
Have never heard any of the T50 mods, so I didn't mention them, but I also don't intend my list to be comprehensive. I'm sure there's a number of closed headphones that will vaguely fit into this criteria though (hell, the original Koss Pro4/A from 1968 will fit into this criteria, and leave around $550 in beer money).