In simplest terms, try to remember this. In order of importance, it's:
3. DAC, custom cables, earpads ect
Always start with #1 the headphone. Spend as much as you can to get the sound that you want with the headphone first. Secondly amps can make a pretty big difference. Get an amp rated to handle the power requirements of the headphones that you bought. Don't always just go for power with an amp. Dynamics, sound stage, transparency are all also important. The dac will make the smallest impact but is still import. I've found the odac to be great with most amps I've owned even high end. It's very neutral and measures well. But there are lot's of good amps and dacs out there. Figure out your budget and listen to and borrow equipment if you get the chance. Don't be afraid to buy used. You can get some great deals, especially with amps and dacs that are like new here.