If you don't plan on using a receiver or any other kind of amp, you will need to by active speakers(active, meaning powered speakers(speakers with built in amps)).
You will only get 2.1 surround since that is what your DVD outputs. Look for active speakers that have an optical input. Many computer speaker systems have optical inputs or if you want a better quality sound you could go for some home audio powered speakers like some on this link.
For example, 2.1 you could get 2 studio monitor speakers and a sub woofer.
Happy Listening, the Prisoner.