You'll only need HDMI for the surround if you are running a blu-ray, or upconvert DVD player along with the surround. When i redid my den, i purchased a Samsung Surround 5.1 1000 watts with built in blu-ray hooked up with hdmi to the TV, but it was $800. For $400 or less you can get a 1000W system with upconvert DVD player, and it'll be a good one.
Don't just get the speakers, you'll need something with an amp to provide the power for the sub, and provide you with surround.
I have also seen some built in blu-ray theatre systems for around $600.
You will not use the AV2. You will use HDMI 1 for your HD cable/Sat reciever and HDMI 2 for your surround w/DVD upconvert/Blu-ray and HDMI 3 for playstation 3 or xbox.