piggyback zones in whole house audio

Im thinking of adding a Russound or Niles whole house audio system to my house. I can pretty much justify a 4 zone system. However, I would like to have a zone in my basement. That puts me at 5. Can I double up a zone? Say put the garage and basement on one zone? Would I loose independant volume control between the two? I typically listen to the radio when Im doing any type of work so extra sources arent needed.
Couldn't you just add an inexpensive receiver/amp? You can buy decent ones for under $100 if you don't need processing (5.1, etc).