80% of your audio in a 5.1 system goes thru the center channel speaker. So, that is where you should spend your money on a good one. You did not mention a subwoofer. If you have no sub you can't have a 5.1 system. Bookshelf speakers are usually only good for the surround in a 5.1 system and the surround back channels in a 7 .1 system. You can get a pretty good new 5.1 speaker system for $400-$500 plus $200-$300 for an HDMI A/V receiver. Of course, the sky is the limit if you want to go high end. Hope this helped.All 5 of the same model bookshelf speakers or 4 of the same model and a center channel speaker?