I can't be of much but will opine in any case. I have heard the Polks and while generally liked them, in some ways a lot, they perhaps have the slam you are seeking but simply did not have the transparency to keep my interest. Haven't heard the others but the woofer on the LS50 is small. R300 has a slightly larger woofer. I have a pair of Q300s in my second system and they are satisfying. Decent bass, wide image, good transparency. I woould expect the r300 to exceed them in every way.