We define a notion called almost strict domination for pairs of representations ρ1 : π1(Sg,n) → PSL(2, R), ρ2 : π1(Sg,n) → G, where G is the isometry group of a Hadamard manifold (X, ν). We prove that ρ1 almost strictly dominates ρ2 if and only if one can find a (ρ1, ρ2)-equivariant spacelike maximal surface in the pseudo-Riemannian manifold (H × X, σ ⊕ (−ν)), which is unique up to fixing certain parameters. Adapting a construction of Tholozan, we construct all such representations and parametrize the deformation space.When (X, ν) = (H, σ), we establish a correspondence between a family of maps into (H × H, σ ⊕ (−σ)) and anti-de Sitter structures on Seifert-fibered 3-manifolds. In this way, we show that an almost strictly dominating pair gives rise to a Kleinian anti-de Sitter 3-manifold. Moreover, we can extract geometric information about the 3-manifold using maximal surfaces and associated Higgs bundles. The general results on maximal surfaces allow us to parametrize a deformation space of anti-de Sitter 3-manifolds as a union of components in a PSL(2, R) × PSL(2, R) relative representation variety, analogous to classical Teichmüller spaces.