charley,
Here are some pics of how I did mine. Hopefully this says it all, but if you need some specifics email me.
Like Chris said, I used a 6" PVC end cap, but I made a wooden insert and attached it to the PVC with screws. I then had something to screw the actual speakers on too. The wires go straight down the pole and then out a different hole near the bottom of the pole. After the wires came out of the pole at the bottom, I added a simple cannon plug (radio shack) so that I could remove the pole whenever I wanted. I found all of the hardware and grommets and stuff at a local home improvement store.