You should NEVER do squats with your heels elevated! That's a dumb idea, but that's also another thread in and of itself.
I'd choose another ham exercise, not feet higher on the leg press. You are still pushing w/your quads in that movement, and if you truly annihilated your quads CORRECTLY with squats, you don't want to do ANY more pressing movements. Stiff leg deads or 1 legged ham curls w/an accentuated negative, or hyperextension static holds.
Do as you wish, you want to superset, be my guest. What do I know with my "theories"?
~SC~