The Stanton m.304
seems to have all the connection that you need, allthough I do not know how it actually routes the sound. Obviously you've connected the send to the input of the EFX-1000
and the return on the output. Set the in/output level switch to +10dB.
Make sure that both rotaries (input and output adjust) are opened and both effect switches are in OFF position.
On the 304 I can only see the FX button to mention, I guess it will send the signal through the send/return when activated. Which signal is routed through the send/return (before or after the EQ/Fader/Xfader) and is it inserted or does it mix the send/return signal is dependant to the electronics of your mixer.
If you've followed above description and the EFX still doesn't receive a signal it must be a operations issue with mixer...