You get no bread with one meat ball.
You get what you pay for. That cable box is free with Comcast basic cable. You have to connect it to the antenna "F" connector on the back of your TV and use channel 3 or 4. Forget about going through the receiver. Considering that 's RF only, it doesn't work too bad. Dunno if it passes HD, though.
If you want the better outputs you'll have to spring for a more expensive package from Comcast.
Actually, that's not a RGB (Red/Green/Blue component), connection. That would be three RCA jacks, generally in the respective colors, and would be ideal for your situation. We have a Comcast/Mototola HD box that uses RGB component connections and it outputs 1080i quite clearly.