So I'm needing a new pair of open-back headphones. I'm looking at a budget of around $150. I've been looking at HD598, DT990, or AKG K612. But for the K612 and DT990(and DT990 are a bit pricey) I would need an amp, so if I did go this route is there a good CHEAP amp that would support them? From what I've heard the HD558 are very similar in sound to the HD598, so would the 598 be worth the extra $35? The headphones would be used for music, gaming, watching twitch/youtube, etc. Another question is, is ebay a reliable source? I've heard mixed things.