"I also question why REL manufactures their subs with such low wattage? For example, their S3 delivers only 400 watts and their T/9i's deliver just 300 watts. When comparing them to subwoofers like JL, which deliver 750 watts to $1500 watts, maybe REL subwoofers are just too wimpy.,
Power is not what makes deep, convincing bass. A combination of construction and location do more than the gimmick of massive wattage specs.
Have you ever heard a quality 5 watt tube system at full steam? Close enough to concert level for most ears.
If you're not hearing the difference when the sub(s) are off, then they calibrated incorrectly. The overall sound quality would be immediately noticed, when turned off.
IMO, even the finest speakers in a great room, will SUBJECTIVELY sound more convincing with properly adjusted subwoofers.