To test your surround sound speakers use a 5.1 surround test file from Lynnemusic available here.
To test the frequency response of your audio system use the free audio sweep generator available from David Taylor here. I reccommend listening to a 20Hz to 20kHz slow loop. I find it easy enough to pick out highs and lows in the response but if you want to hear the "ideal" version test your system with a good set of stereo headphones first. Just remember that your high frequency hearing starts dropping off very significantly after the age of 25.
I had to use both of these tools recently to set up a new set of 5.1 speakers that came with a wildly over enthusiastic subwoofer. Some carefully placed padding and duct tape calmed down the subwoofer and the sweep generator allowed me to check that I hadn't done too much damage to the overall frequency response.