I will echo the sentiments already expressed here. I would try turning off the sub entirely and setting the speakers to large, at least until you can get the better sub. Also, definitely leave the EQ off, or at least check it for sanity. It's not always a foolproof thing, as you've discovered.

With everyone's combined knowledge here, I'm sure we can all help get you set up optimally before too long. Hang in there! \:\)