Heres a basic rundown of options you have:
http://www.audioholics.com/home-thea...or-large-homes
You have a few options starting with a range extender:
http://www.amazon.com/NETGEAR-N300-W...eless+extender
I havent used an extender personally but you could try that first if you wanted to see if it can boost signal to the other parts of the house.
Since extenders can slow things down after they repeat and you only have a 5Mbps connection, you could also run an Ethernet line from your theater room upstairs. You should be able to pop a line up through the floor or wall and make an outlet in the kitchen. Maybe in a cabinet someplace you can then place your Belkin and make it a Wireless access point. Read over the article and you can then see what your options are.
You could also just get a more robust wireless access point that may reach all parts of the house. Then just turn off wireless on the Actiontek and use the new access point to give wireless. Usually the ones that come from a provider arent that great. And the Belkin 150 is not that great either in terms of range.
http://www.amazon.com/EnGenius-Techn...n%3A2888517011
We have 4 similar to this model in our office here, and they cover well and can be used as power over ethernet, so you dont even need a power source at the actual wifi unit.
http://www.amazon.com/Ubiquiti-UniFi...n%3A2888517011