Baseball Sound System

Hey jd, these folks have helped me in the past, and are going to help again pretty soon. I deal with Bob Phelps. He's listed under the "meet the staff" link. I'm sure he'll be glad to advise you.
http://www.customlightandsound.com/

For what it's worth: We use a mixing board, kept indoors, with speaker wire leading out to 4 speakers mounted approximately 20' high on the backstop poles, with two cables running from the mixing board to the scorer's table, where I plug in my laptop. One plug goes into my computer for the music, the other connects to the microphone for the PA. The whole system stays in place except the microphone and the computer, which I bring to and take from games. I found outdoor all weather speakers via googling. They've been up 4 years, all year round, and no issues. I use Real Player to play the music.

p.s. Speakers were around $175.00 each. Mixing board has been in the light room forever; I think Edison must've built it...but it still works.