Well I've amped a Cowon S9 before, and I'll be honest, I didn't notice much difference, the bass tightens up a little and you gain more volume (louder) the soundstage become slightly wider, there is more power there, all this will depend on the amp you're using. but overall you're only adding a second device to charge and a brick to carry around.
As I said, I don't think you can wrong trying a E6, to grab a feel of what's going on. They're only about $25. A small price to pay before jumping on something like T1. You will still get a drift of the concept and what's going on. The Cowons are good players and they have decent DAC's but they're still in the mainstream for mp3 players, there's a lot better out there.