I will reiterate the recommendation of using a DAC/amp like the uDac. Together with the Shure 940 you can have a high quality portable laptop system. The AKG 70x is not the right headphone. I've owned 3. It's too demanding with it's need for a powerful amp. The PortaPro is fair at best. I've owned it. And just about every headphone mentioned in this thread.
The reason I suggested the Shure 940 is because it does well out of the laptop or an iPod. It's a closed headphone so it works well if isolation is needed. For a closed 'phone it manages to sound more like an open 'phone compared to most other closed cans. It also performs above it's price.
The reason I suggested the Shure 940 is because it does well out of the laptop or an iPod. It's a closed headphone so it works well if isolation is needed. For a closed 'phone it manages to sound more like an open 'phone compared to most other closed cans. It also performs above it's price.

