Frequency reponse on those speakers is 46hz to 26khz, so, bass and thickness may be lacking to your ears... Try pushing them closer to the front wall and farther away from the side walls. This should increase bass and reduce any reflections present. Also try toeing them in or out, depending on how they are currently set up.
Note: Usually for full range towers you want the low range frequency response down to approx. 21hz... so, as others have said, a subwoofer may be the fix.