With my 350, when I used my VT as the preamp I plugged the unit into the effects return. It worked great. Now with the 500, I did that...got no sound. Plugged into the power amp in...and it was enormous, but it seemed like it defeated all the panel controls which made the VT the sole controller like a old school amp w no preamp gain or master... the level control handled all the volume. Is this hooked up right?