I've been using MDR-V6 headphones for ages (which are the same thing as the 7506), and they don't need an amp, they sound just fine out of portable gear and laptops.
Keep in mind some portable gear and laptops have very cheap outputs, so if you have a cheap DAC or headphone amp that is really low power, you might want to grab some better kit there, but you really don't need anything elaborate.
iPhone/iPod Touch/big iPod - good output
iPod nano/shuffle - not so powerful
Apple MacBook Air, MacBook Pro - great output (at least the ones I have)
Some people have mentioned older MacBooks are weak, and many PCs have lousy outputs.
If the cans are sounding good, you're fine, these are extremely easy to drive and super efficient.