FWIW, I upgraded the sub in my living room system last year. I went from a BIC F-12 to a SVS SB-2000. The BIC is pretty comparable to the Polk you’re looking at. There’s just no comparison between the two subs. The SVS is cleaner, can be crossed over at a higher frequency if needed, is more...
When it comes to subs on a budget, my opinion is that better is better. A lot of people seem to disagree. But two lesser subs just play slightly louder then one lesser sub. A better sub is simply better.