I recomend Moonshell 2
It runs on every flashcard but you need a dsi compatible one. Moonshell 2 gives you the ability to listen to music, read text and even write, watch videos and view pictures. Overall everything a DSI should be able to without a flashcard.

I think if you download Moonshell 2 from the official site you´ll be given a bunch of tools and one of it is a standart dpg convernter but Im not sure about that since the last time I used Moonshell 2 is 2 years ago. I cant provide a link atm. cuz im in england and im writing this with my 3ds but im sure you find it on your own and if not then wait till saturday then im back home .