Any specf reason your looking at only Wharfedale? Even Taga Harmony Platinum SW-10 v.2 Active Subwoofer is a good choice as of today.
Haven't heard anything going this low on Freqn.
Frequency Response: 20Hz-200Hz
Amplifier Power: 175W RMS / 550W Dynamic Peak, THCA
If interested reach out to FM "efernand1" , he was working on group buy for the same.