In this study, a selectively-doped GaAs/AlAs heterostructure was used to fabricate a high-mobility two-subband electronic system with a substantially different concentration of electrons in the subbands. We observe microwave photoresistance at high numbers of magneto-intersubband oscillations (MISO). The system under study demonstrates microwave-induced resistance oscillations (MIRO) and MISO interference. The MIRO in the studied two-subband system appears in lower magnetic fields compared to the MISO. This is an indication of some additional mechanism that exists in the two-subband system and is responsible for the MISO amplitude damping in low magnetic fields, while it does not affect the MIRO amplitude. Zero resistance states appear in the system under study under microwave irradiation in a narrow range of magnetic fields near the MISO maxima.