If you’re expecting only around 10 inches deep, probably not going to find any serious amount of bass extension. However, some small form speakers these days are pretty amazing relative to size. But if you’re expecting more oomph than what you’ve already encountered in what you’ve already tried you might need a sub hidden somewhere. Just the same…
I was thinking Totem Mites or Silverline Minuets. Both can be found used a a very reasonable price at even just a few years old, but do not extend very deep. Tonally speaking, definite +1 for Harbeth!
I’ve also seen Revel speakers come up in these types of discussions as well. Outstanding designs, most are very linear but expressive. Some of the Focals? Q-Acoustics? Wharfedale Denton 85th’s?