What would be best buy out of the box??

You've made your choice doubly tough by first limiting your choices to the HT-in-a-box solutions, most or all of which aren't very good, relatively speaking, and then making it even tougher by giving yourself just a $300 budget.

If you already have good speakers that you're happy with, I would probably build a component system a piece at a time, starting with a receiver that has the input/output connectivity options, output power, and other features that you want.

I would agree with the last post. There is nothing out of the box that is truly worthwhile for any price, in my opinion. For the price you described, it would be difficult to get a decent receiver. However, if you go used, you may be able to find something on e-bay or some similar website. If you want a nice system and cost is an issue, build it slowly beginning with a nice receiver. You could then find a speaker system out of the box that could work.

If the area that you will play media is relatively small, you can spend less money and go 50-75 watts per channel RMS. Larger areas should be at least