Absolutely ditch the current subs. The room is too big, and they are…not very useful as subwoofers. The specs are atrocious for subs and in fact, my mains go lower. Invest in a quality pair of 15’s or 18’s from HSU, Rythmik, PSA, monolith etc. quality bass is an investment, and as you’ve found out, filling a good sized room is not easy.