Lots of bass at walls, lack of bass in center of room/listening position@smodtactical This is the classic description of a standing wave in the room.
While room treatment will help a little bit, its effect is marginal. You have two solutions both of which will work fine, depending on how you want to handle this.
The first is as others have suggested, move your subs around until you find a location that allows you to hear bass at the listening position. This can be tricky but can be done even with only one sub.
Now if you think you might want to hear the bass properly in any position in the room, then you need to break up the standing waves. The only way to do that (you can't do it with room treatment) is to use multiple subwoofers. You'll need at least 4 to do the job. This type of subwoofer approach is called a 'Distributed Bass Array' and is very effective- with the qualification that none of the subs operate above 80Hz. But its likely that your main speakers go lower than that, so this should be fairly easy. Below 80Hz your ear cannot tell where the bass is coming from- and the harmonics of the bass instruments will make you think that the bass is coming from in front of you.
Two of the subs would be placed in front of you, and the other two placed asymmetrically in the room, with one maybe on one side wall and other other in the rear on the opposite side. You might get better results by putting one of the latter two out of phase with the rest. They can all be fed a mono signal- again, if kept below 80Hz this will work fine. To get bass evenly distributed at all frequencies this is the most elegant approach. There is one subwoofer that is built specifically for this purpose, the Swarm, made by Audiokinesis in Texas. Good Luck!