Xantech 686-10 is what you need.

I'm not sure why you think you would need to demolish/rewire your whole house to do a true multi-room system though. Do you have Volume controls in each room? If so, look into Matrix Audio. Keypad zoned control over existing speaker leads...

If not, you already have the and IR system in place that sounds like its working in your situation.... You could control the Multiroom with that... B&K CT-600 had separate IR codes for each zone..... I'm sure there are other options as well.