Are the router and wireless router on different subnets? What is an example IP address of your TiVos and your PCs? The TiVo Beacon (or Bonjour) won't traverse subnets, so if TiVo Desktop is on a different subnet from the TiVos, they won't see it.
You could try connecting your PC with TiVo Desktop to the same switch as the TiVos and see if Music and Photos appears.
You could try connecting your PC with TiVo Desktop to the same switch as the TiVos and see if Music and Photos appears.