  Let $\Gamma_n(\mathcal{\scriptstyle{O}}_{\mathbb{K}})$ denote the Hermitian
modular group of degree $n$ over an imaginary quadratic number field
$\mathbb{K}$ and $\Delta_{n,\mathbb{K}}^*$ its maximal discrete extension in
the special unitary group $SU(n,n;\mathbb{C})$. In this paper we study the
action of $\Delta_{n,\mathbb{K}}^*$ on Hermitian theta series and Maass spaces.
For $n=2$ we will find theta lattices such that the corresponding theta series
are modular forms with respect to $\Delta_{2,\mathbb{K}}^*$ as well as examples
where this is not the case. Our second focus lies on studying two different
Maass spaces. We will see that the new found group $\Delta_{2,\mathbb{K}}^*$
consolidates the different definitions of the spaces.
