A Selle SMP TRK saddle cured the crotch numbness for me, and is the most comfortable seat I've ridden, both on upright and drop-bar bikes.
Bigger tires at a lower pressure help. I went from 23mm at 100/105 psi to 28 mm at 80/85 psi on my road bike.
Cinelli cork/gel bar tape helps somewhat. Exactly how you place your hands and how often you vary the placement makes a difference too, for me at least.
I actually have a ShockStop stem. I used it in a rather Franken carbon bullhorn setup which was quite comfortable. I had to use the lower-stiffness rubber inserts to feel it working, perhaps because the carbon bullhorns had a fair amount of flex by themselves.
Really, do try the Selle SMP TRK. It's like a crotch cradle.
Selle SMP TRK