We show that a polynomial p with no zeros on the closure of a matrix unit polyball, a.k.a. a cartesian product of Cartan domains of type I, and such that p(0) = 1, admits a strictly contractive determinantal representation, i.e., p = det(I - K Z(n)), where n = (n(1),...,n(k)) is a k-tuple of nonnegative integers, Z(n) = circle plus(k)(r= 1)(Z((r)) circle times I-nr), Z((r)) = [z(ij)((r))] are complex matrices, p is a polynomial in the matrix entries z(ij)((r)), and K is a strictly contractive matrix. This result is obtained via a noncommutative lifting and a theorem on the singularities of minimal noncommutative structured system realizations.