We consider an auxiliary spectral problem originally introduced by Gerdjikov, Mikhailov and Valchev (GMV system) and its modification called pseudo-Hermitian reduction which is extensively studied here for the first time. We describe the integrable hierarchies of both systems in a parallel way and construct recursion operators. Using the concept of gauge equivalence, we construct expansions over the eigenfunctions of recursion operators. This permits us to obtain the expansions for both GMV systems with arbitrary constant asymptotic values of the potential functions in the auxiliary linear problems.In case ǫ = +1 the matrix g belongs to the group SU (3) (g † = g −1 ) and when ǫ = −1 to the group. Further on we shall use the general notation SU (ǫ) referring to both cases, i.e. it implies SU (ǫ) ≡ SU (3) when ǫ = 1 and SU (ǫ) ≡ SU (2, 1) when ǫ = −1.Since g(x) ∈ SU (ǫ), the values of S(x) will be in the orbit O J0 (SU (ǫ)) of J 0 with respect to SU (ǫ) (it is a submanifold of isu(ǫ)). Thus S(x) ∈ O J0 (SU (ǫ)) ∩ g 1 where g 1 is the space of the matrices X in sl (3, C) such that HXH = −X, see (15) for the reason for this notation. Let us also note that conversely, if we assume that S(x) ∈ O J0 (SU (ǫ)) ∩ g 1 then on the first place S has the form as in (1). Next, as easily checked, the eigenvalues of the matrix Sare µ 1 = 0, µ 2 = −µ 3 = ǫ|u| 2 + |v| 2 .But since they coincide with 0, ±1 we must have ǫ|u| 2 + |v| 2 = 1. Our approach to the GMV ± system will be based on the fact that it is gauge equivalent to a generalized Zakharov-Shabat auxiliary systems (GZS systems) on the algebra sl (3, C), see section 3. Generalized Zakharov-Shabat systems, called Caudrey-Beals-Coifman (CBC) systems [2] when J is complex, are probably the best known auxiliary linear problems. In their most general form they are written on an arbitrary fixed simple Lie algebra g in some finite dimensional irreducible representation and have the form:Here, q(x) and J belong to g in some fixed representation, ψ belongs to the corresponding group. The element J must be such that the kernel of ad J (ad J (X) ≡ [J, X], X ∈ g) is a Cartan subalgebra h J of g. The potential q(x) belongs to the orthogonal complement h J ⊥ of h with respect to the Killing form: