There are only two IR addresses available to given receiver model, for HD dvrs's and R22 SD dvr, the codesets are 00001 & 00003. For standard receivers, SD dvrs, and HD receivers, the codesets are 00001 & 00002. So if you had the right combination, you could possibly control them all via IR. But if the are all the same, forget it.
If they are RF remote controllable, then you can have as many receivers as you wish set to RF.
What are the model # of the receivers?