theoretically, the answer to your first question and your second question is, yes.
A big misconception that a lot of manufacturers want us to believe is that you must get their sub to best match their speakers. Any quality sub will integrate with just about any quality speakers. This is ahuge generalization and for the vast non-audiphile majority of us it holds true.
Yes you can get a sub that has a lot more output ability than your mains, but too powerful is a bit of misconception. You can simply turn down the sub to the point where it blends with your mains. Now of course it doesn't make much sense to go out and buy a Velodyne $12,000 DD1812 to go with a pair of $50 Sony bookshelves. For a decent system, buy a sub that costs about as much as your mains. If you are building a 2.1 stereo system or a 7.1 system the formula stay about the same. There are several other variables that come into play like your room size and listening habits. Post a budget, and what you are doing and people in here can help narrow your choices. Best of luck and I hope this helps.
