I should nearly be feeling really ashamed and embarrassed to be back here posting, but I'm not and dont concede to being like that, so here you go.
Think of when you're boxing and you have your hands up under your chin in an opening guard.
This is part of my personal ab regime so i hope you enjoy it.
For the twists, I like to think of that as a very wide hook or back elbow, hand back to or beside chin at the end of each "strike". By thinking of it like that, and using single arm movements, I feel like I get a better rom and stronger wind into my torso. To get to different angles or heights, think of hooks or the back elbows from that position to various points or body parts of a phantom opponent in front of or to the side or behind you.
For the ones between the legs - the reaches, I like to think of them as jabs. With a jab, one would making a 'pouring a cup of tea upside down at "impact " point and quickly back upright as the arm begins to withdraw from the "strike".
With dumbells they are an absolutely kick ass exercise.
You can vary the weights of your Dumbells and the number of reps for each weight and use them for any of the exercises listed above.
As you saw with the fitball, ou can also vary platform heights to do those off meaning you can also incorporate deeper incline and decline motions.
If you really want to take it to a more compound advanced level and can maintain enough form throughout, you can add in DB skull crushers to a two section good morning set, or single and dbl shoulder presses for your overhead reaches in addition to the between the legs "jab" to superset or flys and crosses at different angles across or into your body or single and alternating db lat pulldowns and so on. If you need to you can hook your feet on something to ground.
I'm going to play with this again myself in only a matter of weeks.
I do quite like the other ab exercises you're doing aswell and being they work from different ranges and lengths to what we just spoke about, i would keep them in your regime, even if that meant on alternate days.
Have fun with it.
Blooming tianshi lotus.