I've been trying to remember my eax mixer settings (I retired my Live! ages ago) but I seem to recall that you could set the source for the EAX effects to the soundfont synth. You could choose the source between line-in, mic and synth as I recall.
I found the mixer, but it is rather strange. According to the picture in the instructions there is a possible choice of synth (MIDI synth) as you say. But under the picture they warn you that "Some options are available only with selected Creative audio devices.". In fact, in my mixer there is nothing called MIDI synth, but there instead there is an option of choosing simply "MIDI". Here you can use "advanced controls" in order to select MIDI chorus or MIDI reverb (or both). Any idea of what this means?