There are lots of DVD players made that have 6 RCA outs for 2 mains, 1 center, 2 surround, and 1 sub.
Pair such a DVD player with 5 or 6 amps that have RCA inputs, like the Crown XLS series, and you can run 5.1 surround through a PA system.
As both a KJ and a home theater buff (I have a 180" screen poolside in my backyard), I can tell you that using PA speakers for home theater is pretty much overkill. I run my backyard theater in 3.1 virtual surround off three 60 watt high-fi Sony speakers that cost about $18 each, and it sounds really really good and USUALLY attracts the police.
For a GREAT resource for home theater, especially backyard home theater, check out this site (the link will take you to a guy with a 5.1 surround PA system):
http://backyardtheater.com/forums/index.php?topic=354.0