subwoofer 19 by 18 room

I am building a 5.1 home theatre
have an Arcam 350 on the way and am using B&W Matrix twos, center and 301's in the rear

I've a bit stumped on subwoofer
everything I demo is too loud, rolled wrong and it sounds like a booming box

Definitive, B&W, Martin Logan didn't excite me
Paradign sounded okay, heard stay away from Velodyne (but I was impressed with them 20 years ago)

any suggestions for a single unit subwoofer?
probably need some eq in my near square room

I may even have Jim Salk build me something

ps I have a two channel room where I do my serious listening to music