It's worth your while to acquire Drop 6XX headphones, essentially Sennheiser HD 650s with a different paint job and a much lower price. Here's the rub with any really great transducer---the better they are, the more likely they will expose flaws downstream. The sound of my 6XX's is dependent on the source it's plugged into. So, it's at its best with the Topping E/L 30 combo, playing back Apple Lossless files from a computer. I've got two DAPs, the Fiio M3K dosn't have quite enough power, the Fiio X1 is better in that regard. The smartphone doesn't have enough juice, the computer has juice + distortion. But in addition to all that, the Topping combo sound has better control, better capture of low-level detail. So you can use these 'phones with a fairly wide range of equipment. Some will work better, but the overall character and quality of sound is pretty much the same.