My room is also 28 m2. I have two pairs of subwoofers in the room. Dual vintage REL Storm III’s on the main system, and dual BK XLS200-DF’s on the (near-field) desktop system.
I’d personally go with the BK XLS400-DF, as a single subwoofer, in this size room. Or one of the larger RELs. Check out the recent, vintage-style REL Classic 99.
btw, in case you go with a low-level connection from your HiCap, and unless your cables are quite short, they should be slugged with 100R resistors (100 ohm resistors in series with each of the yellow and red positive leads, I believe).