[Fistulator]

I want to upgrade my computer audio setup, but I don't know where to start. I have a standard crappy sound card but I use my Meier Audio Corda 3Move as a DAC and have a pair of Senn Hd650s. I've just started work on my computer setup. What do you recommend that I get? A new sound card, a better DAC or an amp?
I have about 200 euros to spend, can maybe stretch it a bit and I live in Europe so I need a site can ship there.