If you need louder sound from a DS then amping is okay i think, but just like what Wes008 said, it won't really make it any cleaner.
But from my experience connecting E7 to DS, the sound quality didn't improve that much and all i did (i think) it was just getting louder.
But from my experience, DS audio doesn't only come from the hardware itself, NDS's games have their own kind of audio quality, some are good and some are just okay.. some games would benefit plenty, but not all games. Newer games like The World Ends With You would benefit better than Rune Factory 3, something like that i think.
Enjoy your DS