#2 Any way to reduce very bad rumble without turning the bass so far down that the subwoofer is ineffective?
There are a lot of factors that can go into the "rumble" sound you are describing. A couple things to check would be your low pass knob (recommended ~80Hz), your phase switch if you have multiple subwoofers (set one to 0, the other to 180), and your subwoofer level within your AV receiver (set to +0dB and adjust slowly from there).