I'm coming into this thread really late but don't see why a small soundbar wouldn't work. I haven't tried one myself since I have some great speakers on my desk and a really good sub next to it - but I do use a tiny soundbar with my stand mounted Echo Show 15. I just couldn't take the tinny sound from the tiny built-in rear firing speakers, so I added a
Polk Audio MagniFi Mini (non-Atmos). The only name brand soundbar I could find that's smaller than my Show 15 and fits under it just fine. Not the best speaker that I've ever heard, but a huge improvement over the Show's speakers and it was on a 50% off sale.
The only other place that I've ever used a soundbar is under my 'throne TV'

, so I'm hardly a soundbar expert. What I do like and have owned when space was tight were tiny
Klipsch ProMedia 2.1 speakers and they worked great. The non-BT version even goes on really deep sale every once in a while. Again, they won't compete with a high-buck speaker system with a great subwoofer, but for their tiny size - wow!