  In this paper we consider the following problem: Let $X_k$, be a Banach space
with a normalized basis $(e_{(k,j)})_j$, whose biorthogonals are denoted by
$(e_{(k,j)}^*)_j$, for $k\in\mathbb{N}$, let
$Z=\ell^\infty(X_k:k\in\mathbb{N})$ be their $\ell^\infty$-sum, and let $T:Z\to
Z$ be a bounded linear operator, with a large diagonal, i.e. $$\inf_{k,j}
\big|e^*_{(k,j)}(T(e_{(k,j)})\big|>0.$$ Under which condition does the identity
on $Z$ factor through $T$? The purpose of this paper is to formulate general
conditions for which the answer is positive.
