Eminent technology rotary TRW-17 subwoofer
http://www.rotarywoofer.com/
http://www.soundandvision.com/content/eminent-technology-trw-17-rotary-subwoofer#Lpu6qStoHOLVAQpm.97
regarding the DIY with multiple TCsounds LMS ULTRA 5400 18"'s
Do you have a carpenter/speaker builder who will build the cabinets?
I am looking at a couple of subs as well for one of my rooms and am currently exploring the DIY route with a local custom speaker builder. I could bring him the parts; he builds the cabinet and I or he does the assembly.
One of the cons I can see with this type of approach, if things change down the road - resale.