  We extend the free monotone transport theorem of Guionnet and Shlyakhtenko to
the case of infinite variables. As a first application, we provide a criterion
for when mixed $q$-Gaussian algebras are isomorphic to $L(\mathbb{F}_\infty)$;
namely, when the structure array $Q$ of a mixed $q$-Gaussian algebra has
uniformly small entries that decay sufficiently rapidly. Here a mixed
$q$-Gaussian algebra with structure array $Q=(q_{ij})_{i,j\in\mathbb{N}}$ is
the von Neumann algebra generated by $X_n^Q=l_n+l_n^*, n\in\mathbb{N}$ and
$(l_n)$ are the Fock space representations of the commutation relation
$l_i^*l_j-q_{ij}l_jl_i^*=\delta_{i=j}, i,j\in\mathbb{N}$, $-1<q_{ij}=q_{ji}<1$.
