I have the audio-gd fun with earth opa, and just bought a hd650.... and I highly recommend it. I was after a nice balanced sound with just a bit of bass and not too much treble. The details are all there without being shoved in your face like some brighter headphones I won't mention. Quite euphoric...
BTW I was really worried that people with the HD650 and the Fun were overly enthusiastic about the synergy between them. I kept reading that with a bad amp the hd650's sound dark and muddy etc. and people were often recommending expensive amps (much more than the FUN). I'm definitely not worried anymore. The Fun can handle the hd650's no problem. It definitely does the hd650 justice.
BTW the Fun is on sale for 10% off and it comes with the opa earth free (first time Ive seen it one sale), get version A. Also I bought the HD650 from razordog deals on ebay for $330, awesome deal. With both of those you will be fairly under budget.