Hello everyone! Hope someone can give me some sound advice... I currently listen to AT M50s powered by an ALO "The National" AMP from a Macbook Air via the headphone jack using Fiio cables. I have some money that i want to spend on upgrading the system... but I'm stuck in the middle... Should I purchuse new headphones (He-400s) or rather spend the money on a DAC (Thinking Schiitt Bifrost)? The files i listen to are mostly standard iTunes purchases and Apple Lossless that I ripped from CD's. Thank You!