I have the HFI-780 and the Pro 900. I don't know how much research you've done, but it seems like what you're looking for is the Grado sound (incidentally, I also have the SR-80i which you also have, as well as an SR-325is) in a closed-form. Ultrasones are sometimes referred to as "closed Grados," which is not far off, since both brands tend to have strong treble and an aggressive, forward sound. However, some of your other considerations make me think you might not want to be too set on an Ultrasone, at least not without more research or ideally, testing different headphones out.
The 900 has decent isolation, but the 780 is definitely significantly better at blocking outside sound. In terms of leaking sound, neither does this very much, but 900 a little moreso. It still wouldn't be very noticable unless you played them loudly in a quiet environment.
I don't really think either are the best you can find when it comes to female vocals. Most people don't find them natural-sounding enough, and Ultrasones tend to be suited better to more synthetic genres of music. Of the two, I prefer the 900 though, as the sound quality is more clear and detailed than the 780. I'm perfectly fine listening to something like female vocal trance on the 900, but for more acoustic-based music I'm usually reaching for a can from a different manufacturer.
Coming from the SR-80i, if you are concerned about the amount of bass, you may find both of them overpowering, especially the 900. In that sense, you may be better off with something a little more neutral like the HFI-680, or even something from another brand like the the Shure SRH-840, Sennheiser HD 25-1 II, Fischer-Audio FA-003, or even the new AKG K550.
Edited by LithoJazoSphere - 12/28/11 at 12:18pm