I just want to share some opinions and write a little review.
Everybody knows the SHE-3580 / 3590 and I do too, I loved them until the cable died, so, I had to buy a new pair, but they didn´t have any on stock, only the SHE-3500.
Philips SHE-3500
Overall : Like the 3590, but with a less bass, better treble, and better soundstage.
Construction : The only improvement that you can "see", it´s the tips, they are thicker and I will include some pics tomorrow. I always read complaints about how useless the stock tips were for some people, so, it´s a nice touch. Overall, they look the same, but the metal grill is now something like a "cloth".
Sound : It´s pretty different compared to the 3590. Bass is still there, with nice amounts of sub bass, but more controlled. I recommend using them with a Bass Boost preset or something, and they will sound pretty nice. Treble is the biggest difference, if the 3590 were a bit dark, or veiled, this things are pretty bright. Even with a Bass Boost thing, they will keep sounding bright, maybe too much sometimes, but everything sounds more detailed.
Soundstage is better IMO, I can hear easily the panning effects on the songs, and everything sounds with more separation, sounds wider than the 3590, and that is pretty nice. They could have improved the cable maybe, but the sound is still good and i´m enjoying them a lot now. Treble is not AMAZING, but at least you can hear it easily, it´s a bit harsh sometimes. MIds are still recesed, but it shouldn´t be a problem for peeps that like the V-Shape signature. Overall, I recommend them, basically the best at the price. they doesn´t sound at all like cheap IEM´s.
P.D : My first pair was defective, it didn´t have bass at all, but, I convinced the seller and he gave me a new working pair.