the humped ridge is a great outing. you will find a description in i think the 1958 MCSA journal. basically it follows the right hand skyline when facing the amphitheatre. Those ballies were a bit more hardcore than us and i guess you could find a 'D' grade passage up there but more likely to be around grade 16 in places. you can get down in 3 long rappels.
There is another route to the right of the humped ridge - Kaplan's route from around the same era. also 'D' grade but looks quite complicated.
antoni van heerden opened a grade 16 or so route up teh left hand skyline of the amphitheatre - not sure where this was published but i think in a back issue of sa mountain.
The violet towers that i am aware of are on the other side of the hex river valley - about half way between boskloof amphitheater and milner. a big chunk of rock that rises off the shale band. this is also a great outing at around grade 12, although a moerse walk - a long day's walk from anywhere. it is in one of the old journals too. incidentally the rib that forms the left skyline of boskloof amphitheatre is a splendid 'D' grade outing too. do not contemplate walking up boskloof unless it has been ravaged by a recent fire.
i can give more detailed beta on all these routes, access, dos and water spots etc if you decide to go - same username as forum domain is sim dot sanlam dot com