What exactly are you sourcing from? Is it going to be a dedicated source or are you taking signal off of a home a/v system (like splitting the outputs from a receiver/amp?) are you feeding it pre-amp level that requires seperate amplification to power?
if the source is already at (powered) speaker level u may consider this: (most commonly used in my setups)
http://www.home-technology-store.com/home-audio/C-1001.aspx
or use impedance matched volume controls?
http://www.smarthome.com/8262w.html
Radio Shack makes an inexpesive switch box....? Does it really need to be amplified? you can still install an l-pad at speaker level, probably will be cheaper to do it that way...
there are also many Kits you can buy that will do this for you including L-Pads, speakers, etc... over all these units will work better than the PA amp you found at parts express-- what is the price range/limit you are looking at?