The Pioneer A-40AE has a line output (RCA) that can be used to connect an active subwoofer. This line-out is the appropriate connection as the amplifier itself does not have a dedicated subwoofer output socket with an integrated low-pass filter. You can therefore connect the subwoofer via the RCA line-out and connect the speakers directly to the speaker terminals. This allows 4 speakers and an active subwoofer to be operated simultaneously, with the subwoofer receiving the signal from the line-out.