there are many SM58 wireless systems, depending on what wireless system you are using your output levels and impedance varies. IE in the Shure ULX receiver with the XLR out the signal -17dBu @ mic level but at only 22ohms of impedance. while on the PGX it is -19dBu @ mic level with 22Ohms. I have personally tested the VMS4 with the ULXS receiver and an SM58 if your audio levels RED LEd comes on when you speak in an normal voice adjust the mic gain adjustment on the transmitter (handheld or lavelier) and lowering my volume on the receiver output to about 50% so i can have headroom on the gains of the VMS4. there is also an attenuation switch for LOUD speakers or if you want to sing death metal.The Eq is also there to help you set your tone or cut off unwanted frequencies, not intended to boost your output level. Use the EQ in accommodation to you mic frequency response curve.