HD600 , HD650, HD598 don't qualify according to this.
Try the codes! When I asked, Razordogaudio said that they are good on everything till the end of the month.
Regarding the price on the HD600, I think $300 is a great price. Once a couple years ago, Amazon went lower on a Black Friday deal. The HD600 sells used for close to $300 because normal price is $400.