Spatial multiplexing aided spatial modulation (SMx-SM) is a communication technology which essentially combines the concepts of Vertical Bell Labs Layered SpaceTime (V-BLAST) and spatial modulation (SM). In this paper, we construct a high-rate spatial multiplexing aided generalized spatial modulation (SMx-GSM) scheme which guarantees a very low detection complexity. Benefiting from the codebook structure, a tree-search based MIMO detector for the SMx-GSM scheme can be devised. Simulation results show that the detection complexity can be significantly reduced, which makes a highrate system feasible, and an error performance which is very close to that of the maximum-likelihood (ML) detector can be achieved, especially for the case of a high-rate large-scale SMx- GSM system with a large number of activated transmit antennas.