Low impedance headphones are a relatively recent development, thanks mostly to the rise of the mobile market. In the past most headphones were high impedance. Historically they had to be high impedance because they were being used with hi-fi speaker amplifiers, to which manufacturers often simply added resistance in order to provide a headphone out at reasonable volume. With that in mind, you would routinely be looking at amplifier headphone outputs with impedances in the 50~100ohm range, which forced headphones to have input impedances considerably higher.
High impedance headphones do have a couple of properties that can improve sound quality though, it's not all just a hangover from the past. Having a high impedance allows the headphone to use more turns on the speaker coil windings, which typically means tighter control of the voice coils and cleaner, clearer details. High impedance headphones also require less current to drive and when you combine this with most amplifiers preference for driving higher impedance loads, you end up with less distortion.
Does this mean that low impedance headphones are intrinsically worse than high impedance? No, because it's all realative, it just means that to get the most out of low impedance headphones you have to use an amplifier with a correspondingly lower output impedance. In the case of your Sony MDR-MA900s, you should have no problems at all with any of the very low impedance amps.