Thanks again for all the help.
Actually though, my lack of patience (or maybe the excitment of actually fininshing a project!) got the best of me and I went ahead and fumed my bench with no TA solution whatsoever.
But, I did some new things to help darken the results, and it seemed to help a lot:
1. Use more ammonia. Instead of one small dish, I used one large dish plus two small ones. Clearly created a lot more stink.
2. Aim some heat toward the fuming tent with a space heater. I read that a warmer temp could possibly result in a darker brown, and make the reaction happen faster.
3. Replace the ammonia with fresh stuff half way through the 4-day fuming process.
The result was a nice grayish chocolate color, which my wife actually really liked (more than the reddish brown achieved with the TA.)
Now there is a new problem (which I actually asked about in a new thread) - is there a finish that WON'T darken the fumed wood!? I know, I'm a flip-flopper, but we both like this grayish chocolate color and the wipe-on poly REALLY darkens it a lot (I tested.) Not sure what would deliver the protection needed for a table, without penetrating and darkening... water-based poly?