I tend to listen to indie rock and acoustic-y singer/songwriter music. The occasional jazz. In addition to the 650s, I also have a set of Grado 125s and an AKG 240 Studio. I have also owned etymotic 6p which I used to love (but lost). Prior to the 650s, I had tried out the AKG 702, but found them to be a little cold (although I did not have a proper amp at the time -- I have since gotten the Little Dot MK IV).
I really love the 650s, although might prefer just a touch more treble (I am going to try tube rolling soon).
The closed back cans will be basically a backup for late night listening, maybe subway travel and home recording if I ever get back to that.
The Fischer/Brainwavz (which I'm guessing are basically the same) seem interesting, but I can't find where to buy them in the US?
The KRKs look interesting as well.
Do these take to amping?
The Brianwavz Hm5's preform amazing on acoustic music, very smooth headphones, you can buy them at amazon for 149.00 or mp4nation.com for 119.00, if they're still doing their special sale. Get the Brainwavz if you really enjoy the sound of your HD650, and no they do not need any source of amping, the HM5's and FA003 are extremely easy to drive, you can plug them straight into an ipod, the only benefit you get from amping them is a change in sound stage.