Stew,
It doesn't matter if the different receivers have different codes. The router guarantees that receivers with the same codes will get the right signal to the right receiver. If you have different codes, you can still switch the router to that unit or those units, or even bypass the router entirely if there is only one unit with different codes.

I say this because I am using routers to send signals to multiple Xantech RAT-1 volume controls. I also use the same routers to send commands to two different Fujitsu plasmas and two different Yamaha receivers. One particular RT8 output has a RAT-1, a Fujitus and a Yamaha receiver on it, and the RT8 is simply switched as appropriate. Just as in a system with no IR circuitry at all, the Fujitsu, for example, does not care if it sees a Yamaha or Rat-1 signal.