Can an active subwoofer be connected to a stereo receiver that does not have a MIX/SUB output?
If the stereo receiver does not have a MIX / SUB output, then the available inputs and outputs on the subwoofer will determine whether or not the subwoofer will be compatible.
Check the subwoofer to determine if it has IN and OUT speaker wire connections. If so, connect the left and right speaker wires from the stereo receiver into the left and right speaker IN on the subwoofer. Then, connect speaker wire from the left and right speaker OUT on the subwoofer to the left and right main speakers.
If the subwoofer does not have IN and OUT speaker wire connections, then it will not be compatible with the stereo receiver.