adwarp from +acpc to +tlrc does not work, as you've observed. I actually tried to make it work at one time, 2-3 years ago when this problem arose before, but was unable to get it right in the limited amount of time I spent on it.
One possibility is to use a command like
3dfractionize -vote -clip 0.2 -template anat+orig -input roi+acpc -warp anat+acpc -prefix roiXX
to transform from +acpc to +orig, then do the
adwarp -NN to transform to roiXX+orig to +tlrc coords. Clumsy, but it should work.
bob cox