scientist say that super human strength is impossible because we need more muscle mass but what if we made out muscles denser so there are more...

Muscle strength is a function of a number of factors,
including physiological factors, i.e., size and cross-sectional area as well as
mechanical (pennation or angle of pull and muscle moment arm lengths) and neurological
(neural drive to muscle) factors.

Increasing the density
might be one way to increase strength but, while the force generated by a muscle occurs
within the muscle cell, increased density would come at the cost of reduced space for
other, equally-important components of the muscle, e.g., reduced space for the
sarcoplasmic reticulum, which stores calcium without which muscle contractions simply
could not take place.  Increased density might also mean that the build-up of lactic
acid during sustained contractions might occur faster than could be removed, thus
limiting the ability of the muscle to produce force for sufficiently long periods,
resulting in muscle fatigue.