before you buy the pro logic speaker, i recommend you to rethink and buy true dolby digital 5.1 (or dts 5.1) because it have both the digital optical and coaxial cables jack.
for around 200 - 300, i think you can get a decent 5.1 sound channels. but of course, you need more speakers if you only have 2.....and don\'t forget the subwoofer too!