Does anyone know of any subsonic ammo that will eject the shell and chamber another round?  I tried the TTI armory ammo and although it is subsonic, it didn't have enough power to eject the shell or chamber another round.

That's an interesting question. What is the bullet weight, 55 grain?
Since the energy is related to velocity squared, a 3:1 reduction in velocity would be accompinied by a 9:1 reduction in energy. The energy for cycling also comes from this propelling energy so it is not surprising that it does not cycle.
(these numbers are appoximate, there are other factors involved)
A lighter buffer and spring might help. But it might not have enough force to chamber a new round.

I thought EBR (Engel Ballistic Research) was the shiznittybam when it came to subsonic ammo

Engel Ballistic Research sub-sonic will not cycle either.
As stated at SRT Arms website,
http://www.srtarms.com/ebr.htm

"The ammunition intentionally does not cycle
the action, for the ultimate in quiet shooting.  63-gr. Sierra Match moly-coated
projectile."

I suspect it is just the nature of the stuff.

[url]http://www.extremeshockusa.com/cgistore/store.cgi?page=/new/product.html&setup=1&ida=7&idp=0&his=0&cart_id=6971740.1160[/url]

Thats is what you are looking for, it works flawlessly.  I have several of the original devolpment rounds in my ammo can right now and video of it being fired through both my rifle and a full auto suppressed M16....  just be prepared to pay out the nose for this ammo, like $3 a round.