I have a medium sized room with Polk R50's as the fronts, R15's as the rears, and the CSi20 as a center. I dont have a sub yet and i dont know if I should get a PSW350 or a PSW550. I really like how both sound, but I like how the 550 looks more. Looks arent very important, but I just want a good polk sub, so i can have an all polk system. Which should I get?