How should I setup my new Home Theater system?

5.1 means you have 5 channels to work with. A 285 watt Sub is plenty of power for a home system and -6.0 dB is probably right if the mic set it there. When you used the microphone to set up the surround sound it was checking the reflections of sound off the walls for optimal acoustic settings in relation from receiver to speakers. I would try to use the microphone to set the center and rear speakers too. If all else fails the best thing you can do is listen to the system and set the levels to best balance you can. I know you're not a mixing engineer but your ears are your best tool unless you want to pay for a home instillation, hope this helps, best of luck!