If it helps any, I've seen the 3580 and 3590 in the flesh and they look identical, with identical housings and eartips, apart from very slight changes in color schemes.
Someone wrote Philips and they said the 3570 (generation previous to the 3580, again with different housing colours, but what looked to be different tip material) and 3580 are the same earphones, but I haven't heard the 3570 myself to confirm.
If the 3570 is the same as the 3580 there's a good chance the 3590 is the same as the 3580 too.
On the other hand, I bought the SHH3580, which is a mic'd version of the 3580. You'd think they would sound exactly the same but they don't. The SHH3580 has a less V-shaped response which may actually be better for un-EQed use, although it may not be the best for bass lovers.
I also bought the new SHE3680, hoping they would sound the same as the 3580, and with the better build, bundled headphone case and chin slider. But I could immediately tell a difference between them. Not that either is better or worse, they're just different. Again the 3580 has the more V-shaped sound of the two. I guess Philips may be moving towards a more neutral signature although the 3580 is only considered mildly V-shaped among budget phones.
But even if the 3590 are different from the 3580, I'm sure they will also be very capable earphones. Haven't got a dud from Philips yet. The only reason I'm stocking up on SHE3580s is because I've stuff my mobile phone full of tunes pre-EQed for the SHE3580 on the computer (since I'm not satisfied with any EQ I can find on the phone) so I'd need another pair of phones that sound exactly like the 3580 the day my current pair dies, it's that or re-encode all my tunes for a new pair of phones.
