Universal remotes are great but often rather pricey. If you want to make your own, Make shows you how to use an Arduino Yun to make a smart remote control you can control from any web browser.
Essentially, you're using the Arduino Yun to both communicate with your entertainment center and host a web page where you can control everything. Once you have it set up, you control everything in your entertainment center using a web browser on your phone or computer. Head over to Make for the full guide if you're interested.
Smart Remote Control [Make]