I was able to rumble loose objects on bookshelves with my old Salk Songtowers with their 5" woofers. When I sold them, the new owner (during the audition) asked where my subwoofers were. I don’t own subs. It’s the room.
I’m sure you like the way your system sounds...but I hate to say this: your system/room combo just ’looks like it wouldn’t sound good’. No treatment (simple rug) and as an added insult, framed glass behind each speaker.
The best thing you can do is simply try something. I do think most of us don’t know what we don’t know unless we experience the difference. I really thought for many years that my system sounded perfectly fine until I moved one my LP rack to the opposite side of the room and something immediately changed. The change was stunning and across the whole spectrum and made the bass sound beautiful, focused...and simply stand out like never before.
Sure a subwoofer could help...but first start with putting a rug under your speakers and amoir. If you can, find get a rug that fits perfectly up the the floor/wall boundaries on all three sides and comes out a few feet in front of the speakers. Handmade rugs often come in unusual sizes and I’ve been able to find something to fit every situation.
But just don’t put a cheap/thin rug there. It needs to be on a heavy felt underlayment. This is usually provided by a good rug retailer. These will make a difference.
If you can only hear what you’re hearing. How would you know what would sound better? Try something simple first. Like a rug. Then try removing the framed glass and replacing it with art that has more diffusion/absorption qualities.
It’s tough for us to remember that we’re actually listening to our rooms. If you can’t/won’t change the room, adjust tour expectations and get a subwoofer or two.