You need a power amp that has 1/4" outputs to the speakers (or XLR or speakon depending on the speakers you get). The amp/preamp you linked to appears to only have binding posts for the speakers.
I suggested the mixer, but a preamp or receiver would work as well. My thought was that a...
A couple notes.
John's advice to go with pro audio gear is very good advice in your situation. However, it changes some of your needs. Instead of a receiver, you will now need a mixer and a power amp. Here's a link to a mixer that would probably be appropriate.
You'll also need a power amp...