| I've been using the Presonus Digitube Equalizer with the GK and it works pretty well. Plugging it into the "return" of the effects loop is not so good (in my opinion), it sounds kind of midrangy, but with sufficient twiddling of the parametric knobs I can get a useable sound, and its quite a bit louder before feedback then going into the GK preamp (incidentally I use the Schertler DynB). Going into the pre-amp has a more pleasing sound if I turn down the bass completely, and barely turn on the treble, high mid and low mid. Then I turn the output volume on full (!) and use the "gain" as a volume control. Still, not much volume this way. | 
