Keep the Dominion no matter what.
Consider adding a JL Audio E series which can master RCA output to the Dominion via a pair of long interconnect cables from Blue Jeans or Monoprice Cables.
After performing a crawl test position each sub near your rooms two loudest bass modes.
Can someone comment on the possible advantages of using DSpeaker or MiniDSP subwoofer equalization over Roon DSP?
Then run the equalized / optimized source signal to the E master sub.
Or, wait for a used Velodyne DD-10 Plus as the master for your Dominion.