i beat all 7 stages everytime.
my troops of choice:
terror Island WARRIORS
Terror Volcano HZM, WARRIORS, TMED (all maxed)
usually about 1 in 15 times i can't beat stage 7 then i'll boost GBE MP or TD MP.
the troops you have, i think you have a shot, but i think you really need to boost a few statues. (remember though, both stage 6 and 7 give one guaranteed dark crystal each)
the layout of the base is a HUGE factor. i'll suggest start looking for the ones that don't have shock launchers. they can make the raid very difficult.
check out my youtube site. there are some terror videos in there =)