Many DVDs play both Dolby Digital and DTS. Dolby Digital is usually the default, so you need to go through the DVD's setup menu and change it to DTS. They are both 5.1 channel digital surround sound and send a digital signal to the receiver through the digital/pcm output on the DVD player to the digital input on the receiver. Pro-logic is the old type surround sound. The surround coding come in along with the analog sound through the audio interconnect cables. Pro-logic is still important, because standard television signals that are in surround sound are pro-logic. If you've ever seen at the beginning of a TV show that it is broadcast in surround sound, it is pro-logic.
