When I was back in school...going for all the noise I could I did this trick with two two channel Sony Receivers from my Sony CD player. It worked well for my four years in school. I did have a problem though. If I wanted to just listen to one receiver (the master), I had to have them both on. If I didn't turn on the "slave" the master would have terrible static. The second I turned on the second Rx, it cleared right up...whether I had the "slave" speakers on or not. I fixed this by using a powered splitter...except then I started having digital clipping issues with the newer over mixed CD's (another story). Here is the link to what I used...or I could sell you mine, as I don't use it anymore. Its at radio shack...called a distribution amplifier.
http://tinyurl.com/y8ssmt