Rookie here, I own a pair of ATH-M50s and after doing a bit of research I'm leaning towards the Swans for my desktop setup. I realize the Swans are self powered and, from what I understand, the M50s don't stand to gain too much from an amp.   Looking around a bit with my limited knowledge I haven't been able to pinpoint an ideal DAC/amp unit or combo to get the most of both the headphones and speakers. Any recommendations for under $500, and ideally under $300?...