For a steal (+-R1000), the Sennheiser HD448 has a midrange that punches way above its price range and will suit your requirements of piano and female vocals to a tee. A bit flabby and light on the bass unamped though, but with half decent amplication it really shines! I much prefer it to the HD595 I used to have. From what I've read the HD598 should be a decent improvement on the HD595. I'm just a bit wary at is appears that the design is the same as the older headphone which had build quality issues.
Otherwise for double the price I might suggest an AKG K271! I quite liked Norah Jones with that headphone and it made jazz sound quite spacious and airy which was nice, but I don't think it would do as well for other genres.
On a side note, piano was also one thing I consider the Audio-Technica ATH-M50 to be slightly less adapt at. Made piano notes sound slightly metallic, but apart from that it is a brilliant allrounder and loves a bit of power.
