use rca y splitters .
like this ones
http://cgi.ebay.com/3-RCA-Adaptor-Splitter-1-Male-2-Female-Audio-AV-Plug-/260780543562?pt=LH_DefaultDomain_0&hash=item3cb7bb4e4a
get 2 than put one on each rca on the amp than simply connect the left rca's from the both recievers to the left on the amp and do the same with right rca's
it can be done ive done it before.