I would like to clarify something here regarding the 808's as reading this thread I am quite confused about exactly what the op is asking.
I noticed you indicated what you are using now are 808 threaded but are only that. Does the head of your 808 passthrough look like this:
View attachment 205515
or 808 Ego threaded like this:
View attachment 205516
Because if your 808 passthrough doesn't have the ego threading on it, the Clearomizer X2's from Si will not work.
Or if it is a cigalike - the X2's will fit but not the T3's.