Again, as I didn't get to own both at the same time, I can only recall what I can. To my ears, the treble on both the Pistons and the Philips aren't harsh (in fact, the SHE3590 sounded rather dark). Take note of that, since to your ears, both may turn out harsh. As for the mids, I really cannot say.
Imo the SHE3590 has harsh empasized uppermids and lower treble, and is indeed rather dark. They are normal for the price imo, didn't understand the hype around them.
The only thing that stands out on them is the bass response.
So maybe I should stretch out my budget if the Pistons and the Philips are on the same league...