Some things to try:
Turn off ALL QoS or Disable Traffic Shaping on host router.
Setup DHCP reserved IP addresses for all devices ON the host router.
Ensure devices are set to auto obtain an IP address.
Enable uPnP and Multi-cast Streaming if the host router has this option.
Wireless Installation ConsiderationsWhat wireless modes are you using on host router?
Try single mode G or N or mixed G and N?
Channel Width set for Auto 20/40Mhz or try 20Mhz only.
Try setting a manual channel to a open or unused channel.
What security mode are you using? Preferred security is WPA-Personal. WPA2/AES Only. Does it happen if you turn off wifi security temporarily?
What Wifi speeds are supported on host router?
What wired speeds are supported on host router?
Does the boxee hang if wire connected using LAN?
Try adding a external Gb network wired switch between the router, NAS and Boxee and test.