This paper is devoted to the problem of spectral H_∞-optimal control synthesis for LTI plants. This problem is significant in situations when spectral features of the external disturbance are not completely given. H_∞-optimization problem has been paid very serious attention for the past decades and it can be solved with the help of well-known numerical methods, based on Riccati equations or linear matrix equations (LMI), but these approaches are not absolutely universal, because there are irregular situations, such as problems with no noisy measurement signal. Implementation of the spectral methods, based on parameterization of the set of transfer functions of the closed-loop system and polynomial factorization makes possible to avoid mentioned difficulties, but most of the research in this area are devoted to the plants with scalar control signal that significantly restricts its area of implementation. The approach, proposed in this paper, makes possible to overcome these difficulties. Some theoretical aspects, including matrix Nevanlinna-Pick rational function interpolation, are discussed and computational scheme for the optimal control design is formulated. Applicability and effectiveness are illustrated by the numerical example with implementation of MATLAB package.