well, to route it from 3845 to your asa inside interface, you will need public IP's all the way along, if you dont have that, you could try getting up a GRE tunnel from router to your end device.
with out a little more to go on thats all i could say for now. does your 6500/3560 do any routing? (internal gateways)
do you use private addressing on the asa's outside (front) interface?