I have Polk RTi A5 front speakers with a DSW 440 sub. The sound is nice but sometimes i feel the bass is a little thin. I am not looking for wall shaking, just more presence. At first, I thought about getting a DSW 660 as that is one of the 3 recommended subs on the Polk web site. But I am also wondering if it would be better to get a second 440 instead?