Since it's not working very well for your legs don't be afraid of trying something else. I would suggest doing squats 3 times per week and give it time until the body adapts. You need to give it some time.
Good idea. I'd even go so far as to say to do some legs every day in addition to the 3x/week pounding. I'm no guru, but I know when I have a lagging part (shoulders, triceps) or something I'd like to grow more (legs, abs), if I do my "normal" stuff and every day do something for that part -- that part seems to grow a whole lot more.
So, for example, do your squats/presses/hacksquats on mon/wed/fri. Then on tue/thur/sat do 100 rep leg extensions...50 w/ feet wide/out and 50 w/ feet together.
And, when you do cardio, select the exercises that work your legs the most. Bike sucks. I like the stair-stepper that has actual physical stairs that rotate -- like an escalator with stairs -- NOT the normal stair-stepper because that's too easy to cheat on.
...do this, ESPECIALLY if you're doing any enhancers...even if you aren't, do it for a week or two every month.
Like I said, I'm no guru, but this sort of thing worked for me in the past...