Get a built in sub or get a bigger amp

Right now I have am OHM 5000 Walsh paired with a Bryston 14bsst. I'm on the upgrade path now and wondering what would be a better sonic improvement of the following 2 options. Option 1 to is send my OHMs back and have a 15 inch extreme subwoofer installed with a 500 watt amp in a bigger speaker enclosure and get a smaller Bryston 4b3. Or Option 2 is to get a 14b3. I wonder how much the subwoofer would free up the Walsh driver? Would the cohesion still be there unlike some of the subs in panel speakers have been? I have run the 5000's with a 4bsst before and it couldn't drive them to loud levels that I'm accustomed too. Im intriqued by the Walsh 5015. John S says they can go down to 16hz for some scary bass. The sub powered models have been out for about 5-6 years now but I haven't seen much posted here about them. I hope to hear your opinions., I have a 20X12X8 room that partially opens up to a 10X10X12 room. Thanks
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