I agree with RTI Installer and/or Sirroundsound.

The Nexus Media would work. The RTI system with a matrix switch will get you covered. personally i would take out the VC's and use a matrix that gives you volume control that way the client can control all the volume from the remotes.

This is really a pretty simple upgrade. Just settle down. It sounds like you haven't done a system like this, but this seems pretty straight forward. You just don't have in-wall controls, no biggie.