abs are built by squats and deadlifts
if you want abs, go and grab a barbell and do heavy squats and heavy deadlifts as the bar commands and demands balance and symmetry and because they are both compound exercises not only do they work every single muscle in the body but in turn they spike up a crazy metabolism
theres only one rule i have for you, DO NOT USE ANY WEIGHT BELTS FOR ASSISTANCE, my theory is that guys that use weight belts are not able to lift the weight using their core without that weight belt so the core will not be as strong as the rest of the body, you wont be as lean in the core as the rest of the body and your health will not be as good.
i once watched lee priest the bodybuilder and on an interview he was asked what ab exercises he did to get abs, LEE PRIEST LAUGHED AT HIM, he said he looks after his nutrition, abs are built in the kitchen, when he was pressed further, he said he got abs from the bench press, squats and deadlifts, because he knew how to lift and stoke his metabolism and abs using diet, and lifting.
try playing with your rep ranges so have three separate days where you work on the legs as well and include squats and deadlifts
monday squats and deadlifts working on your 1 rep max
wednesday work on your 6 reps max
friday work on your 12 reps max
for both lifts and include exercises for the rest of the body