Hi,
This is what our club is running:
http://www.thomann.de/ie/swissonic_sa_65.htm
Running multiple speakers, ont rostrum / pits.
(Speakers from same supplier, cost was ~£200.)
It also runs multiple inputs for the mic. We use two, one at beside the computer at race control and one at the bottom of the rostrum, for in race announcements (crashed car / lapping etc.)
A good feature of the amp is that the mic can be set to override an input. So when you are making an announcement over the mic, the input from the computer (race sounds) is reduced in volume. It stops the mic / computer sounds coming over the speaker at the same time and nothing being audible.
Let me know if you want more info on what we went for.
MiCk B. :-)