The solution turned out to be a compromise. I couldn't find what I wanted that would fit in the space, or wouldn't cost 100s of dollars.
What I did find was a nice little little waterproof/bluetooth/usb powered/ plugs into speaker jack, speaker.
It's not a total fix, but the sound from this speaker is much better than from the TV when I have to turn it up. + it's small, so it fits in the space.
Thanks to the Best Buy guy who really knew what was in the store and helped me weed though a bunch of stuff to find this little gem.