The paper is dedicated to a retrial queueing-inventory system with constant retrial rate, heterogeneous customer classes (distinguished by various inventory demands) working under the class- and inventory level-based admission control to a service zone with class-specific servers (one server per class). The replenishment policy is a mixture of the two classical policies, (s, Q) and (s, S). The model is treated by matrix-analytic method in steady- and in transient states in Markov case, and by regenerative simulation in the non-Markov case, and interesting performance measures are derived.