Fred and Julie,

I would also recommend the Matrix Audio solution, Except he said the house was not wired for Volume controls.With no volume control location , there will be no place for the keypad control.
Another thought here: If all the rooms do have a coax cable on the wall, you may use a xantech product and send IR from each room to the main controller. Xtralink2 comes to mind.
If you want to sell them some lighting control too, Vantage and Lutron have RF keypads and controllers with RS-232 interface for either the Elan or Russound. They will get a great lighting system and control of their music from the same keypad!
---end of rambling thoughts.