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Regarding your subwoofer placement, don't worry about a couch being in the way. The frequencies a subwoofer produces are known as omni-directional, meaning you should hear them from all directions. The biggest thing to keep in mind regarding subwoofer placement is that the closer to a corner you place the sub the louder it will typically sound. If you search the forums you'll find many helpful thoughts on proper placement.
Here's a diagram showing the recommended layout for dolby digital:
Your front speakers should roughly have the tweeter at ear level when sitting down, and the rear speakers should be placed to either side of your listening position, ideally about 2-3 feet higher then the fronts. Since it's a 6.1 set up you should place the surround back speaker basically opposite the center channel, also 2-3 feet higher (matching the other surround speakers).
Let me know if you have other questions, and enjoy the sound!