How many speakers can I run on one amp?


I want listen to 2-channel in five different rooms through the house. I'm using a MAC 6700 to run McIntosh XR100's, XR50's, Paradigm 40v Monitors, Paradigm 20v Monitors and some Boston Acoustic exterior speakers.
Is the Niles HSP-6 a safe way to operate and select? They all run at 8ohms and the only speakers I run at the same time are the XR100 and 50. I'm using oxygen free copper 12 ga "audio" wire and some of these runs are 50 feet from the amp.
Is there a better way to do this? Is my equipment safe? 
kenlewis
Here’s a link to the Niles manual: (http://resources.corebrands.com/products/FG01038/pdf_FG01038_HPS-6_manual.pdf) Page 3 addresses your question.  It seems, though the manual covers two models, the text only addresses the four pair version.