Even the 350 will play plenty loud in an average size room, probably louder than you need. What it won't do is reach quite as low as the 500, so will have less impact on movies. I am willing to bet that the 350 will play as loud as the 500 as I believe they both have the same driver and cabinet. The difference is that the EP500 uses dsp (a form of eq) and more power to reach lower than the 350.
The thing with subs is that in order for a one to hit those low notes, particularly stuff below 20Hz, it needs a fair bit of displacement.
So, if you are in a small room, but want a sub that plays down to 15Hz, you need the same bigass sub that would fill a very large room. You just cant hit 15Hz with a 10" driver.
