I am basically only going to receive money for Christmas this year, so I'm probably going to buy the HD650's. What would be a good starting amp/dac for the HD650?
Please provide us with a budget.
My first suggestion would be the JDS Labs ODAC+O2 amp combo, but it costs around $300. This is an amp and DAC combo that you will probably find yourself not needing to upgrade for years to come.
What device do you use to conduct more of your listening? If the PC is the answer then a USB DAC is a must unless you have a decent soundcard already.