Subwoofers can be extremely sound quality enhancing. On of the most notable thinks is to extend the sound stage. But proper integration take effort and knowledge. Just indiscriminately fiddling with the volume and crossovers or randomly moving around the room is unlikely to do the job.
I am attaching an outstanding video where professionals discuss sub woofers with the theoretical foundation for sound in a room. Applicable for full range speakers, and subwoofers in a two channel or home theater situation.