Just a notice, that I personally don't recommend amps to people until they get into the $150+ range of headphones and that are non portable
However a 'good' amp can make it 'better' but the ROI is generally much lower on these.
To more seasoned users of amps and budget headphones. We use amps/DACs with cheap sub $100 units every now and then because we have a few laying around. And because we are just remotely 'flavoring' the sound a bit.
It's easy for people more 'into' the hobby to do this and it may provide a bad picture towards new commers to see us using expensive units with $100 headphones.
Anyway, what do you want an amp to do to your experience with the Sony? More bass? Are you looking for more 'quality' or volume (please don't tell me it's volume)..
If you just need a bit more bass, take a look at the E6 (it won't break the bank). If you want a bit more quality, I would say to save up the money, possibly sell or return the DJ100s and get another can.
It isn't until we get into the $200 range (for newbies) that I recommend newcommerns start getting into DAC/Amps. It's pretty much the path that gives a good ROI for having a can that probably will reciprocate its 'quality' to a nice amp/DAC.
Don't base buying an amp off veterans using them with every device possible.... I probably set a bad example