As most people do at first when they begin to get into Hi-Fi, I think you are approaching this from the wrong angle. Most people buy good headphones, then they realize they need an amp, so they buy an amp, then realize they need a better source. After that they spend money on silver cables.
First, start with a source and cables, then an amp, then headphones/speakers. That being said, I'm really happy with my Little Dot Micro+ and my silver cables. Look on eBay for "Little Dot Micro".
Try the amp with your current headphones first, then go for the gusto, and if you need new cans, pick up some new ones. I might reccomend some Beyerdynamic DT770s they should have a familier sound to you if you listen to sony headphones.
After that, if you feel like it, pick up some silver cables from wherever is local to you, I bought supplies to make some from qables because I'm in Europe. If you build them, remember: Think three times, test fit twice, solder once. Silver cables make the diference. I was suprised when I switched out the gold tipped copper cables for gold tipped silver ones.
Welcome to Head-Fi. Hide your credit cards now. Honest.