Summary: No amp necessary, unbeatable genre bandwidth, very fun and impressive at first contact, but you soon find out that the A900 is only solid midfi. The level of detailling is quite poor, and the mids are -typically for a closed fon- recessed. I had an old DT531 at the same time and definetely preferred the latter in every respect. The A900 isn't exactly a bad fon, but far too expensive. A reasonable bang-for-the-buck ratio would be around 100$ IMO.