You may be able to flash your 655 with the 1.11 firmware, which would take care of nearly all of the reliability issues you're having. If you need stability more than you need cutting-edge features, it would be a great way to go. In other words, don't think of it as a "downgrade" if a particular edition of firmware meets your needs, despite its age.
Regarding your XBOX, take a look at your router's setup, and locate its DHCP range setting (http://192.168.0.1 -> login -> Setup -> Network Settings -> DHCP IP Address Range). If you've never changed it, the setting should be 192.168.0.100-192.168.0.199. On the XBOX, set it to an IP address OUTSIDE that range (e.g. 192.168.0.10 subnet 255.255.255.0 gateway 192.168.0.1).
Also check the router's UPnP setting (Advanced -> Advanced Network -> Enable UPnP). Make sure it is checked, click on save settings, and reboot the router. The XBOX will make extensive use of that feature.
GOOD LUCK
edit: EddieZ always gets to the punchline. I decided to make something a bit bolder than originally written...