https://hometheaterreview.com/sumiko-s9-subwoofer-reviewed/?page=2
When you consider the actual improvement it can deliver to an audiophile two-channel system (especially one employing small to mid-sized tower speakers or large bookshelf speakers), how little effort it will take on the listener’s part to gain that improvement, and that it won’t detract from the sound quality of the main system, it’s probably one of the best buys a subwoofer-less audiophile could make...
and, Sumiko compared to REL:
my experience leads me to suspect that few, if any, unbiased listeners would express a clear preference for one of these subs over the other.