I have the kef 2005.2 and would like help on setting the sub. On the back of the sub there is a a switch and I can have it on either slope 12db or 24db which of the 2 would you recomend I have it on? My volume on my amp is normally -20. I also notice there is a switch for ground in and out which I dont know what it means. I have some knobs saying adjust level crossover frequency and phase adjust. My bedroom is 12ft by 10ft can you recomend on what levels I should have these on please and what they do.